Psalms 33:21

For our heart shall rejoice in him
Not in sin, nor in themselves and in their boastings, all such rejoicing is evil; but in the Lord, "in his Word"; as the Targum is, in the essential Word of God, Christ Jesus; in his person, righteousness, and salvation; and this joy is heart joy, inward joy, real joy, joy in the Holy Ghost; and is unspeakable and full of glory. This is what the psalmist calls upon the saints to do, in the beginning of the psalm; and so his end in composing it is answered;

because we have trusted in his holy name;
that is, in himself, who is holy, just, and good; and so faithful to every word of promise, to every engagement of his, and therefore to be trusted in: and hence it appears that the joy before spoken of is the joy of faith.