Gurfateh
Respected Satya Ban Ji,
Har Har Mahadev and Jai Shri Ram.
As per our Faith Salvation is in the Hand of Akal.
Anyone be it even non Beliver can get salvation as Akal wants.
Das himself worshipped Shiv ling not long before while he was hindu.
Akal wanted to salvage Das so he become Sikh.
Das was not writing it to you but to other two members who are after you.
We have a sort of ailment in us that many of us think that anything before Guru Granth Sahib was wrong and all after them will be wrong as they known the way of Prtestants or Arya Samajis who does the same with Holy Vedas or Holy Bibles.
This is good to the person like Das who Follow Sanatan Sikhism as thier offesive words ward of neo convertts to Faith and no one even thier coming generation does not follow them.
ihn Vedas also term Rudra is used but for formless.
Das just wants to say that Actual Shiva is Akal or Allah who is also Called Yehova and is God of Sikhs.
at the stage of Salvatioin while being alive that is seen in all absorbed anf nothing but that so no form as all form are of that.
Old Sanatan Dharam Scriptutres likie Veda,Upnishads and Holy Puranas justify that.
das is at yuor side
With the coming of Adi Guru Granth Sahib we are able to get the correct meaning of old scriptures also correctly as they(Adi Guru Darbar) are vaste and say nothing is impossible and all is relative but Akal/Allah/Shiva/Yehova/Ram.
So puting that it is contradictory to others shows our lack of knoweldge towards them.
And as Triya Charitar were mentioed here so did Das wrote about them(which you off course do not know).
At last Das only wanted to prove that as per Sanatna Dharam Scriptures
True God is Omni obsorbed.Brahman ,Vishnu and Mahesh are creations.
varous Brahmas,Vishnus or Shmbhu/Shankers wrere various humans with some titltes,Guru got that in Dasham Granth 300 years before present days Sanskrit Shoolars and more then being spritualism they were more humanly.
the Shiva which gave form to Vishnu who made Brahman from Lotus from Nabh of his stomach and Brahma who made Rudra/Shiv Sanker/Sambhu etc.
so Shiv which we worship is light and eternal and not the won which lives a man on Kailash takes form or destrroys the world but rather itself can be destroyed.
Das recomendes you to have faith in your Shiva and if Real Shiva wants you will Shiva's willing know the truth some day.
Best of luck