Some basic information from a reliable source about One God whose Name is Truth. What follows is part of a very interesting article on the subject of the Oneness of God at http://www.searchgurbani.com/gurus/gurugranth.htm
GURU GRANTH SAHIB BEGINS UNIQUELY:
In Hindu mythology the word 'OM' always meant for God as monotheistic. Then they started interpreting it as more than one God. Guru Nanak put an integer '1' before it and a kar (a semi- circle) after it. Thus it becomes 'EK-OM-KAR' and by doing so, he sealed the position for ever meaning 'There is One and only One God'. Therefore Guru Granth Sahib uniquely begins with integer One ('1'). The One Absolute is the monotheistic conception of God and is represented by numerical symbol here. One God does not only mean numerically one but Unique without a second like Him.
Guru Granth Sahib begins with Mool-Mantar or the Preamble of Japji which is the Essence of the whole Guru Granth Sahib: Ek-Onm-Kar Sat-Nam Karta-Purkh Nirbhao-Nirvair Akal-Murat Ajuni, Saibhang Gurparsad "There is But One God He is the Eternal Truth The Creator, All-Pervading Divine Spirit Unfearful, Without hate and enmity Immortal Entity Unborn, Self-Existent Realized by His Own Grace (the Guru)."
The next verse is generally called Sach (True) Mantar:Jap Aad Sach Jugad Sach Haibhi Sach Nanak Hosibhi Sach "Meditate upon Who was True before the Creation Who was True in the beginning of Creation Who is True now, and O Nanak, Who shall be True for ever."
Guru Arjan Dev had accomplished a task by authenticating the diverse compositions and prepared the Adi Granth for the benefit of his followers. Since the work had remained where it was left, Guru Gobind Singh included in it the Bani of Guru Tegh Bahadur and put the seal of Finality on it. Subsequently this finalized version of the Adi Granth was invested with the Guruship by Guru Gobind Singh.
Guru Granth Sahib is the only refuge for a man tossed about in the furious ocean of worldly existence. It helps a person to live by certain directives or moral codes which are necessary for the achievement of salvation.
Man is the epitome of God's creation. This human body is attained after transmigrating through various lower species. Guru Granth Sahib advocates the excellence and utility of human life because it is through human form that a person can attain final emancipation. Man has great capacity for conscious awareness which helps him reach the desired spiritual goal. Therefore, all teachings and exhortations for spiritual enhancement are addressed to man in Guru Granth Sahib. Man's material values are listed as false, 'koor':"False are kings, false their subjects, false the whole world; False are mansions, false palaces, false those who dwell therein; False is gold, false sliver, false he who weareth them; False husbands, false wives, they pine away and become dust. Man who is false, loveth what is false, and forgetteth the Creator. With whom contact friendship? The whole world passeth away. False is sweetness, false honey, in falsehood shiploads are drowned- Nanak humbly asserteth- Except Thee, O God, everything is thoroughly false." (Asa di Var- Slok Mohalla 1, p-468)
Guru Granth Sahib signifies the importance of Nam by identifying it with the Guru. Nam releases man from all his previous sins, sorrows, sufferings and cycle of birth and death. No rituals, no alms, no sacrifices, no fasts and no penances equal Nam.
Guru Granth Sahib initiates a disciple on the path of spiritual progress and guides him at the various stages of his journey to God. It is a ship that steers clear a devotee through the ocean of Maya (Materialism), thus, leading the human soul to its ultimate destination which is the Absolute Bliss.
"The fearful ocean of the world is dangerous and formidable; it hath no shore or limit, No boat, no raft, no pole, and no boatman; But the true Guru hath a vessel for the terrible ocean, and ferrieth over him on whom he looketh with favor." (Sri Rag Mohalla 1, p-59)
Guru Granth Sahib is completely authentic and is preserved in its original form. It is a highly valuable possession which Sikhs have received from God through Guru Nanak and is held in supreme reverence by them.