John Gill Commentary Psalms 75:9

"But I will declare for ever, I will sing praises to the God of Jacob." — Psalms 75:9 (ASV)

But I will declare for ever
These are not the words of the psalmist, but of Christ, who is all along speaking in the psalm; what he would declare is not expressed, and is to be supplied in sense thus; either that he would declare the wonderful works of God, (Psalms 75:1) , so the Targum, his thoughts, mercies, and kindnesses to his people, as in (Psalms 55:5) , or his judgments on his enemies, whom he shall pass sentence on, which will be for ever; or the name of the Lord, his purposes and decrees, his counsel and covenant, his mind and will, his Gospel and the truth of it: see (Psalms 22:22) ,

I will sing praises to the God of Jacob ;
the covenant God of his people, Christ's God, and their God; of his singing praise to him, see (Psalms 22:22) .