John Gill 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
Of the glories, excellencies, and perfections of his person; of his offices, as Mediator, King, Priest, and Prophet, the Saviour and Redeemer; of his works of creation, providence, and redemption; of his word, the blessed truths and comfortable doctrines of it; of his providential dispensations, and gracious dealings with his people in the present state; which to meditate upon, when grace is in exercise, is very sweet, delightful, and comfortable. The Targum renders it as a petition, ``let my meditation be sweet before him;'' that is, grateful and acceptable to him:

or, as the Septuagint and Vulgate Latin versions, "let my speech", discourse, colloquy, address in prayer; see (Psalms 141:2) , or, "let my praise", so the Arabic and Syriac versions: the spiritual sacrifices both of prayer and praise are acceptable to God through Christ; and the speech of the church, and every believer, whether in the one way or in the other, is sweet to Christ, very pleasant and delightful to him, (Song of Solomon 2:14) .

I will be glad in the Lord :
the Targum is, ``in the Word of the Lord;'' in the essential Word, the Lord Jesus Christ; in his person, the greatness, glory, beauty, and fulness of it; in his righteousness, its purity, perfection, and perpetuity; in his salvation, being so suitable, complete, and glorious.