Please see the below two articles from Sikhism101.com, both are extremely good answers
Article 1
What is Sach Khand?
Sach Khand ("Realm of Truth") is the Sikh concept of Liberation from the cycle of birth and rebirth. It is achieved by the Guru's Grace and through meditation and Simran, remembering the Divine. There are two understandings of Sach Khand in accordance to Gurbani. The first is Sach Khand as a spiritual state of being liberated whilst alive through immersing oneself in the Divine Truth and becoming inseparable to the Truth (i.e. God's Light). The second is Sach Khand as a spiritual realm or spiritual place where the blessed souls go after death.
----- UNDERSTANDING SACH KHAND AS A SPIRITUAL STATE OF PROGRESSION -----
Once a devotee attains Self-realization, he becomes situated in this final realm of Truth (Sach Khand), the ultimate stage of Spiritual experience of linking with the Absolute. Sach Khand is a state of mind that you enter when you are alive. It is a state beyond duality or description, a state of Eternal Wonder and Light, which can neither be made to order or give to an another person as a gift. It can be known only in personal experience. It's also called in the Gurbani "Chautha Pada" (Fourth State) because it is beyond three qualities of Maya. Some other names for it include "Sehaj Avasthaa" or "Turiaa Avasthaa" (Supreme State), "Param Anand" (Bliss), "Jeevanmukti" (living liberated), and so on. It is a state of existence in which the soul (Aatma) of the individual is linked and united with the Parmaatmaa (Supreme Soul), like a drop of water in the ocean.
ਸਚੁ ਮਿਲੈ ਸਚੁ ਊਪਜੈ ਸਚ ਮਹਿ ਸਾਚਿ ਸਮਾਇ ॥
"Meeting the True One, Truth wells up. The truthful are absorbed into the True Lord."
(Ang 18)
At this point, the pure devotee or seeker has become one with God within. Here, he identifies himself with the One True, Formless, Infinite Consciousness. Linked with his Origin, the Absolute Reality, his Soul links with the Spirit just as rivers merge with the ocean. This is the journey of an Spiritual aspirant. This journey begins from a material plane and ends at the Spiritual Plane.
----- UNDERSTANDING SACH KHAND AS A PLACE OR REALM OF SPIRITUAL BEING -----
According to Japji Sahib, God is formless and his realm is Sach Khand. Just as the sun resides in one place but its rays are everywhere and felt everywhere, so is the nature of God. When God created Creation, He placed His jot or His light within it. Creation has his light within it and so it is not separated from him. When someone becomes spiritually enlightened through Naam, the light of God is seen from creation as well. Guru Raam Daas Sahib Ji says:
ਜਿਉ ਸੂਰਜੁ ਕਿਰਣਿ ਰਵਿਆ ਸਰਬ ਠਾਈ ਸਭ ਘਟਿ ਘਟਿ ਰਾਮੁ ਰਵੀਜੈ ॥
“As the rays of the sun spread out everywhere, the Lord pervades each and every heart.”
(Ang 1326)
According to Sikhism the ultimate goal of a Sikh is Sach Khand which is far greater than any heaven(s), as believed by other religions. It is a state of union with God in which the soul forever enjoys spiritual bliss rather than physical pleasures like the heaven(s) of the Bible, Quran or Tohrah.
The beginning of the concept of Sach Khand can be in the fact that Guru Nanak Sahib Ji has first talked of this place. Bhai Gurdas Ji says that Guru Nanak Sahib Ji was called to Sach Khand and given Naam from God himself and then the mission to spread this path of Naam (Gurmat).
ਬਾਬਾ ਪੈਧਾ ਸਚ ਖੰਡ ਨਾਨਿਧਿ ਨਾਮ ਗਰੀਬੀ ਪਾਈ ॥
"Baba (Nanak) reached Sach Khand (the Realm of Truth) where from he received Naam, the storehouse of nine treasures and humility."
(Bhai Gurdaas: Vaar 1, Pauri 24)
Guru Nanak Sahib Ji himself writes about this calling to Sach Khand or "Mehal" in this shabad:
ਪਉੜੀ ॥
ਹਉ ਢਾਢੀ ਵੇਕਾਰੁ ਕਾਰੈ ਲਾਇਆ ॥
ਰਾਤਿ ਦਿਹੈ ਕੈ ਵਾਰ ਧੁਰਹੁ ਫੁਰਮਾਇਆ ॥
ਢਾਢੀ ਸਚੈ ਮਹਲਿ ਖਸਮਿ ਬੁਲਾਇਆ ॥
ਸਚੀ ਸਿਫਤਿ ਸਾਲਾਹ ਕਪੜਾ ਪਾਇਆ ॥
ਸਚਾ ਅੰਮ੍ਰਿਤ ਨਾਮੁ ਭੋਜਨੁ ਆਇਆ ॥
ਗੁਰਮਤੀ ਖਾਧਾ ਰਜਿ ਤਿਨਿ ਸੁਖੁ ਪਾਇਆ ॥
ਢਾਢੀ ਕਰੇ ਪਸਾਉ ਸਬਦੁ ਵਜਾਇਆ ॥
ਨਾਨਕ ਸਚੁ ਸਾਲਾਹਿ ਪੂਰਾ ਪਾਇਆ ॥੨੭॥ ਸੁਧੁ
"Pauree:
I was a minstrel, out of work, when the Lord took me into His service.
To sing His Praises day and night, He gave me His Order, right from the start.
My Lord and Master has summoned me, His minstrel, to the True Mansion of His Presence.
He has dressed me in the robes of His True Praise and Glory.
The Ambrosial Nectar of the True Name has become my food.
Those who follow the Guru's Teachings, who eat this food and are satisfied, find peace.
His minstrel spreads His Glory, singing and vibrating the Word of His Shabad.
O Nanak, praising the True Lord, I have obtained His Perfection. ||27||Sudh||"
(Ang 150)
So it is clear that Sach Khand is a place. It is clearly not a place that is "physical" in that of course it has no rules of physics or matter, but it is in fact a spiritual realm. It has been described in Gurbani as a palace like that of a King or Guru Sahib's Darbaar.
ਵਡਾ ਤੇਰਾ ਦਰਬਾਰੁ ਸਚਾ ਤੁਧੁ ਤਖਤੁ ॥
ਸਿਰਿ ਸਾਹਾ ਪਾਤਿਸਾਹੁ ਨਿਹਚਲੁ ਚਉਰੁ ਛਤੁ ॥
"The Darbaar of Your Court is glorious and great. Your holy throne is True. You are the Emperor over the heads of kings. Your canopy and chauree (fly-brush) are permanent and unchanging."
(Ang 964)
Guru Sahib has said that describing this place is impossible. The only accounts we have are from Satguru Ji. A description of this place is:
ਸਹਜ ਸਿਫਤਿ ਭਗਤਿ ਤਤੁ ਗਿਆਨਾ ॥ ਸਦਾ ਅਨੰਦੁ ਨਿਹਚਲੁ ਸਚੁ ਥਾਨਾ ॥
ਤਹਾ ਸੰਗਤਿ ਸਾਧ ਗੁਣ ਰਸੈ ॥ ਅਨਭਉ ਨਗਰੁ ਤਹਾ ਸਦ ਵਸੈ ॥੬॥
ਤਹ ਭਉ ਭਰਮਾ ਸੋਗੁ ਨ ਚਿੰਤਾ ॥ ਆਵਣੁ ਜਾਵਣੁ ਮਿਰਤੁ ਨ ਹੋਤਾ ॥
ਤਹ ਸਦਾ ਅਨੰਦ ਅਨਹਤ ਆਖਾਰੇ ॥ ਭਗਤ ਵਸਹਿ ਕੀਰਤਨ ਆਧਾਰੇ ॥੭॥
ਪਾਰਬ੍ਰਹਮ ਕਾ ਅੰਤੁ ਨ ਪਾਰੁ ॥ ਕਉਣੁ ਕਰੈ ਤਾ ਕਾ ਬੀਚਾਰੁ ॥
ਕਹੁ ਨਾਨਕ ਜਿਸੁ ਕਿਰਪਾ ਕਰੈ ॥ ਨਿਹਚਲ ਥਾਨੁ ਸਾਧਸੰਗਿ ਤਰੈ ॥੮॥੪॥
"Through the Praises of the Lord, devotional worship, spiritual wisdom and the essence of reality, eternal bliss and the imperishable true place are obtained. There, in the Saadh Sangat, the Company of the Holy, the Lord's Glorious Praises are sung with love. There, in the city of fearlessness, He dwells forever. ||6|| There is no fear, doubt, suffering or anxiety there; there is no coming or going, and no death there. There is eternal bliss, and the unstruck celestial music there. The devotees dwell there, with the Kirtan of the Lord's Praises as their support. ||7|| There is no end or limitation to the Supreme Lord God. Who can embrace His contemplation? Says Nanak, when the Lord showers His Mercy, the imperishable home is obtained; in the Saadh Sangat, you shall be saved. ||8||4||"
(Ang 237)
Sach Khand is a spiritual place of bhagti (devotional worship) and true knowledge. Sach Khand is a place of total bliss and is eternal. The Saadh Sangat (company of the Holy) resides there forever and they are carefree. This Saadh Sangat is continuous there. There is no death or fear. There is only bhagti and bliss and they live on the sustenance of kirtan. They sit in the presence of Waheguru and enjoy the bliss forever.
Another description in Gurbani is:
ਸੁੰਨ ਸਮਾਧਿ ਗੁਫਾ ਤਹ ਆਸਨੁ ॥ ਕੇਵਲ ਬ੍ਰਹਮ ਪੂਰਨ ਤਹ ਬਾਸਨੁ ॥
ਭਗਤ ਸੰਗਿ ਪ੍ਰਭੁ ਗੋਸਟਿ ਕਰਤ ॥ ਤਹ ਹਰਖ ਨ ਸੋਗ ਨ ਜਨਮ ਨ ਮਰਤ ॥੩॥
"They sit there, in the cave of deep Samaadhi; the unique, perfect Lord God dwells there. God holds conversations with His devotees. There is no pleasure or pain, no birth or death there. ||3||"
(Ang 893)
This shabad describes the spiritual state of someone who has reached Dasam Duaar (the tenth spiritual gate of the body) and in that state they can experience Sach Khand and see Waheguru in conversation with his Bhagats (devotees).
Finally:
ਸੂਹੀ ਮਹਲਾ ੫ ॥
ਸੂਖ ਮਹਲ ਜਾ ਕੇ ਊਚ ਦੁਆਰੇ ॥ ਤਾ ਮਹਿ ਵਾਸਹਿ ਭਗਤ ਪਿਆਰੇ ॥੧॥
ਸਹਜ ਕਥਾ ਪ੍ਰਭ ਕੀ ਅਤਿ ਮੀਠੀ ॥ ਵਿਰਲੈ ਕਾਹੂ ਨੇਤ੍ਰਹੁ ਡੀਠੀ ॥੧॥ ਰਹਾਉ ॥
ਤਹ ਗੀਤ ਨਾਦ ਅਖਾਰੇ ਸੰਗਾ ॥ ਊਹਾ ਸੰਤ ਕਰਹਿ ਹਰਿ ਰੰਗਾ ॥੨॥
ਤਹ ਮਰਣੁ ਨ ਜੀਵਣੁ ਸੋਗੁ ਨ ਹਰਖਾ ॥ ਸਾਚ ਨਾਮ ਕੀ ਅੰਮ੍ਰਿਤ ਵਰਖਾ ॥੩॥
ਗੁਹਜ ਕਥਾ ਇਹ ਗੁਰ ਤੇ ਜਾਣੀ ॥ ਨਾਨਕੁ ਬੋਲੈ ਹਰਿ ਹਰਿ ਬਾਣੀ ॥੪॥੬॥੧੨॥
"Soohee, Fifth Mehl: His Mansions are so comfortable, and His gates are so lofty. Within them, His beloved devotees dwell. ||1|| The Natural Speech of God is so very sweet. How rare is that person, who sees it with his eyes. ||1||Pause|| There, in the arena of the congregation, the divine music of the Naad, the sound current, is sung. There, the Saints celebrate with their Lord. ||2|| Neither birth nor death is there, neither pain nor pleasure. The Ambrosial Nectar of the True Name rains down there. ||3|| From the Guru, I have come to know the mystery of this speech. Nanak speaks the Bani of the Lord, Har, Har. ||4||6||12||"
(Ang 739)
This great palace is a place of happiness where the Bhagats reside. Inside Guru Sahib describes how sweet this sight is. The Sants there always do kirtan (sing the praises of the Lord) and enjoy the bliss. There is no birth or death or sadness or anything else and amrit naam rains down. Only through Satguru Ji has this place of spiritual being been discovered.
Guru Nanak Sahib Ji experienced the Sat Sangat (true congregation) in Sach Khand. Guru Ji has blessed us on this earth by creating Sat Sangat here with the same Bani he heard there. Bhai Gurdaas Ji says:
ਸਤਿਗੁਰ ਸੱਚਾ ਪਾਤਸ਼ਾਹ ਸਾਧ ਸੰਗਤ ਸਚੁਖੰਡ ਵਸਾਯਾ ॥
"The true Guru is true emperor who has founded the abode of truth in the form of the Saadh Sangat, the congregation of the saints."
(Bhai Gurdaas: Vaar 7, Pauri 1)
The analogy of the sun is given by Gurbani to explain the nature of Waheguru.
ਜਿਉ ਸੂਰਜੁ ਕਿਰਣਿ ਰਵਿਆ ਸਰਬ ਠਾਈ ਸਭ ਘਟਿ ਘਟਿ ਰਾਮੁ ਰਵੀਜੈ ॥
“As the rays of the sun spread out everywhere, the Lord pervades each and every heart.”
(Ang 1326)
In that stage of Dasam Duaar, this can be seen and the sights of Sach Khand can also be seen while living in this body.
Sachkhand does not mean annihilation. It is not a state of nothingness. The soul is merged but not destroyed. Once again it's hard to talk of things like this. But this is clear to me from Gurbani which tells us:
ਗੁਰਮੁਖਿ ਆਵੈ ਜਾਇ ਨਿਸੰਗੁ ॥
"The Gurmukh comes and goes without fear."
(Ang 932)
Bhagat Ravidas jee when describing Sach Khand says:
ਬੇਗਮ ਪੁਰਾ ਸਹਰ ਕੋ ਨਾਉ ॥ ਦੂਖੁ ਅੰਦੋਹੁ ਨਹੀ ਤਿਹਿ ਠਾਉ ॥
ਨਾਂ ਤਸਵੀਸ ਖਿਰਾਜੁ ਨ ਮਾਲੁ ॥ ਖਉਫੁ ਨ ਖਤਾ ਨ ਤਰਸੁ ਜਵਾਲੁ ॥੧॥
ਅਬ ਮੋਹਿ ਖੂਬ ਵਤਨ ਗਹ ਪਾਈ ॥ ਊਹਾਂ ਖੈਰਿ ਸਦਾ ਮੇਰੇ ਭਾਈ ॥੧॥ ਰਹਾਉ ॥
ਕਾਇਮੁ ਦਾਇਮੁ ਸਦਾ ਪਾਤਿਸਾਹੀ ॥ ਦੋਮ ਨ ਸੇਮ ਏਕ ਸੋ ਆਹੀ ॥
ਆਬਾਦਾਨੁ ਸਦਾ ਮਸਹੂਰ ॥ ਊਹਾਂ ਗਨੀ ਬਸਹਿ ਮਾਮੂਰ ॥੨॥
ਤਿਉ ਤਿਉ ਸੈਲ ਕਰਹਿ ਜਿਉ ਭਾਵੈ ॥ ਮਹਰਮ ਮਹਲ ਨ ਕੋ ਅਟਕਾਵੈ ॥
ਕਹਿ ਰਵਿਦਾਸ ਖਲਾਸ ਚਮਾਰਾ ॥ ਜੋ ਹਮ ਸਹਰੀ ਸੁ ਮੀਤੁ ਹਮਾਰਾ ॥੩॥੨॥
"Begumpura, 'the city without sorrow', is the name of the town. There is no suffering or anxiety there. There are no troubles or taxes on commodities there. There is no fear, blemish or downfall there. ||1|| Now, I have found this most excellent city. There is lasting peace and safety there, O Siblings of Destiny. ||1||Pause|| God's Kingdom is steady, stable and eternal. There is no second or third status; all are equal there. That city is populous and eternally famous. Those who live there are wealthy and contented. ||2|| They stroll about freely, just as they please. They know the Mansion of the Lord's Presence, and no one blocks their way. Says Ravi Daas, the emancipated shoe-maker: whoever is a citizen there, is a friend of mine. ||3||2||"
(Ang 345)
In the last stanza Bhagat Ji says that the Bhagats (devotees) can come and go as they please and there is total freedom there.
This explains the army of Shaheed Singhs that many Gursikhs have experienced. These Gursikhs are special souls that have been given this seva (service or duty) and they come on this earth as well.
Article 2
The claim that all paths lead to the same goal is covered in Bhai Sahib Randheer Singh Ji’s book ‘Anhad Shabad Dasam Duar - Open discussion of unstruck ethereal music at tenth door of abode-divine’, pages 46-47:
"The Liberation-state of Gurmat is unique and different in concept from other religious faiths. Liberation is not the mere ending-up of the human body or just an escapement of the soul from its bodily cage. Some envisage liberation as riddance from afflictions associated with the human body. They believe liberation is unattainable as so long as the soul is caged within the human body. Others identify liberation as the fulfillment of their desires to abide in a heavenly abode. However, this kind of liberation falls very short compared to the Gurmat concept of liberation. Liberation is not the banishment of imagined pain and sorrow, nor can it be described as the disassociation of the soul-being from materialism. Yogic faith conceives liberation as empty consciousness through meditational practices that bear no semblance to the Gurmat concept. Vedantic faith believes in the removal of duality to arrive at oneness with The Absolute, in order to be liberated. Buddhism believes liberation to be a state of total renunciation of desire and negative thought - Nirvaana. Jainism considers that non-violence and non-killing leads to liberation. Mere escape from transmigration is not the essence of True Liberation....
Gurmat considers the above listed forms of liberation as halfway and incomplete. The swan-bird Gurmukhs who are blessed with Divine Enlightenment reject all these forms. They merge with The Divine Immaculate Light whilst living; they envision The Glorious Lord in full Divine Splendour.
Gurmukhs are sustained by the nourishment of Naam-Divine, while they behold The Lord at all times. They find True Liberation within this Love-Divine...Their Liberation lies in the sole occupation of Naam-Devotion, in accordance with Gurmat. This supreme state is reached through complete dedication, when one takes refuge within The Guru...what is not sought is a form of liberation devoid of God-Realisation."
If we use this viewpoint to analyse some mainstream schools of thought, we may reach the following conclusions:
In Hindu or Vedantic traditions, Liberation = various states according to different schools i.e. freedom from transmigration, realisation of self as God (Sohang) etc.
In Buddhism, Liberation = realisation of the nature of self/ escape from desires/ Nirvaana.
In Judaism, Christianity, and Islam, Liberation = heavenly abode/ paradise
In Sikhi, Liberation = absorption into Vaheguru/Naam, the destruction of self/ego, the merging of Aatma (soul) into ParAatma (Universal Soul) - all of which can only be achieved through complete dedication to The Guru's Teachings.
The concept of equality exemplified by Sikhi is not the result of a debate concerning which paths are more (or less) efficient and ultimately productive; equality is not based upon such rational discussions or language games. The Sikhi concept of equality is an inward and outward acceptance of all and seeing everyone as a soul rather than religious labels, which results directly from the practice of Sri Guru Granth Sahib jee's teachings.
When it comes to true enlightenment, or liberation, Guru jee is very clear about its unique nature and definition within Gurmat; and in doing so we are taught who and what really is The True Teacher.
Sri Guru Granth Sahib jee over and over stresses the importance of "Gurmat Naam". Without Gurmat Naam no one can merge in Vaheguru or reach ‘Sach Khand’ (the spiritual state of Truth). In the House of Guru Nanak only Naam is found, the only tool to experience and merge into God.
ਏਹੁ ਅਹੇਰਾ ਕੀਨੋ ਦਾਨੁ ॥
ਨਾਨਕ ਕੈ ਘਰਿ ਕੇਵਲ ਨਾਮੁ ॥੪॥੪॥
“God has given this gift. Nanak’s home is filled with only Naam, the Name of Vaheguru. ||4||4||
(Ang 1136)
Without Naam, no one can be liberated and merge with God. Gurbani is clear about this fact:
ਸਭਿ ਸੁਖ ਮੁਕਤਿ ਨਾਮ ਧੁਨਿ ਬਾਣੀ ਸਚੁ ਨਾਮੁ ਉਰ ਧਾਰੀ ॥
ਨਾਮ ਬਿਨਾ ਨਹੀ ਛੂਟਸਿ ਨਾਨਕ ਸਾਚੀ ਤਰੁ ਤੂ ਤਾਰੀ ॥੯॥੭॥
“Those enshrined the True Name within their heart, those within is the flowing current of Naam, and those whose consciousness is attached to the vibrations of the Guru's Baani obtain all comforts and liberation from Maya (the illusionary world). O Nanak! Without the Naam, no one is saved; You too swim across to the other side this true way in which there no chance of drowning. ||9||7||”
(Ang 1013)
Sikhi is unique by the fact that it does not condemn others to Hell or say if you are not Sikh you are eternally damned. Rather a Sikh prays at least twice daily for "Sarbat Da Bhallaa", meaning the good and prosperity of all Humanity regardless of religion, belief or faith.
ਨਾਨਕ ਨਾਮ ਚੜਦੀ ਕਲਾ। ਤੇਰੇ. ਭਾਣੇ ਸਰਬੱਤ ਦਾ ਭਲਾ।
"May the Divine-Name preached by Nanak be exalted. May all prosper and be blessed within Your Will."
(Daily Sikh Ardaas)
All faiths will get what they work towards. Guru Nanak Sahib jee is the only True Guru who has preached Naam, and given Gurmat-Naam. Only Gurmat has a concept such as Sach Khand and God-Realisation in such a clear way. Thus, Gurmat is the only path to Sach Khand, i.e. merging with God.
