John Gill Commentary Psalms 118:28

"Thou art my God, and I will give thanks unto thee: Thou art my God, I will exalt thee." — Psalms 118:28 (ASV)

You [are] my God, and I will praise you
These are the words of David, asserting his interest in God as his covenant God; and which is the great blessing of the covenant, and the greatest happiness of men, and will always continue; and for which there is abundant reason for praise: it is an instance of distinguishing grace, all evidence or everlasting love, and the foundation of all comfort and happiness here and hereafter;

[you are] my God, I will exalt you ;
and call upon others to join with me in it, as in (Psalms 118:29) . The Targum is, you are my God, and I will confess before you; you are my God, and I will praise you, said David: Samuel replied, and said, Praise, O you congregation of Israel; who are addressed in the next words.