John Calvin Commentary Psalms 43:4

"Then will I go unto the altar of God, Unto God my exceeding joy; And upon the harp will I praise thee, O God, my God." — Psalms 43:4 (ASV)

And I will go to the altar of God. Here he promises to God a solemn sacrifice, in commemoration of the deliverance he would obtain from him; for he speaks not only of the daily or ordinary service, but by mentioning the altar on which it was customary to offer the peace offerings, he expresses the token of gratitude and thanksgiving that I have mentioned.

For this reason, also, he calls God the God of his joy, because, being delivered from sorrow, and restored to a state of joy, he resolves to openly acknowledge such a great benefit. And he calls him the joy of his rejoicing, so that he may more splendidly present the grace of his deliverance.

Regarding the fifth verse, I have already addressed it sufficiently in the preceding psalm, and therefore I consider it unnecessary to speak of it here.