It ought to be particularly noticed, that it is no ordinary token of gratitude which he promises, but such as God required for rare blessings; namely, that the faithful should come into his sanctuary, and there bear solemn testimony to the grace which they had received. The design of public and solemn thanksgiving is, that the faithful may employ themselves in all variety of ways, in serving and honouring God, and that they may encourage one another to act in the same manner. We know that God’s wonderful power shone forth in the protection of David; and that not only by one miracle, but by many. It is, therefore, not wonderful that he brings himself under obligation, by a solemn vow, to make open and public profession of his piety and faithfulness towards God.
John Calvin, Commentary on the Book of Psalms, trans. James Anderson (Bellingham, WA: Logos Bible Software, 2010), 1.378–79.
David, as a man after God’s own heart, is a model and encouragement for God’s people. He grieves over the sin with which he has offended God, trusts in God’s gracious promises for deliverance, and gives thanks by his acts of piety and and faithfulness, for the undeserved grace that he has received from God.