Albert Barnes Commentary Psalms 104:34

"Let thy meditation be sweet unto him: I will rejoice in Jehovah." — Psalms 104:34 (ASV)

My meditation of him shall be sweet—That is, I will find pleasure in meditating on his character and works. See the notes at Psalms 1:2. It is one of the characteristics of true piety that there is a disposition to think about God; that the mind is naturally drawn to that subject; that it does not turn away from it when it is suggested; that this fills up the intervals of business in the daytime, and that it occupies the mind when wakeful at night (Psalms 63:6).

It is also a characteristic of true piety that there is pleasure in such meditations; happiness in thinking of God. The sinner has no such pleasure. The thought of God is painful to him; he does not desire to have it suggested to him; he turns away from it and avoids it .

It is one of the evidences of true piety when a man begins to find pleasure in thinking about God; when the subject, instead of being unpleasant to him, becomes pleasant; when he no longer turns away from it, but is aware of a desire to cherish the thought of God and to know more of him.

I will be glad in the Lord—That is, I will rejoice that there is such a Being; I will seek my happiness in him as my God.