Gur means Dhan-Dhan Paar Braham Pita Parmeshwar Ji and Bani is His word. GurBani  means the Shabad that has come directly from God.   Dhan-Dhan SatGuru Sachey Patshah Sahibans Ji were Puran Sant SatGurus, so whatever they  said is the word of God that is why it is called GurBani, meaning the word of God.  Therefore, please take these divine words of the Guru are the word of God as there is no difference between God and the Guru.   The entire GurBani is the Mahima of Akal Purakh, His Naam, His Sants and Bhagats.  GurBani is the language of Sach Khand.  It is Puran Sat, that is why it is called Nirankaar and Guru because Sat is the Guru.  GurBani is also called Shri Guru Granth Sahib, Shabad Guru, Bani, Gyan Guru and Gur Mat.   In summary, GurBani:-

• is the description and the praise of the Mool Manter which itself is the description and praise of the vital qualities of Eternity (God),
• tells us what happens to us when we follow this Eternal Truth,
• tell us what happens to those souls who get absorbed in this Eternal Truth,
• tells us that those souls are the Temple of Truth,
• tells us that such souls have full access to the Brahamgian (divine wisdom),
• reach the Sach Khand (God, the Realm Of Truth),
• become one with the Eternal Being  and
• become His very own Form (Roop). 

GurBani is the language of Sach Khand and it has come from Sach Khand, therefore, for a normal person it is not possible to feel the depth of this Gyan Sarovar.  But, as our Bandgi progresses, our understanding of GurBani will keep on improving and when we are blessed with Puran Braham Gyan then GurBani will become very clear.