John Calvin Commentary Psalms 21:1

"The king shall joy in thy strength, O Jehovah; And in thy salvation how greatly shall he rejoice!" — Psalms 21:1 (ASV)

The king will rejoice in thy strength, O Jehovah! David could have given thanks to God in private for the victories and other significant favors which he had received from Him; but his intention was to testify not only that it was God who elevated him to the throne, but also that whatever blessings God had conferred upon him benefited the public good and the advantage of all the faithful.

In the beginning of the psalm, the believing Israelites express their firm conviction that God, who had appointed David to be king, had undertaken to defend and maintain him. It therefore appears that this psalm, like the preceding one, was composed to assure the faithful that God's goodness toward David in this respect would be enduring. It was also necessary, for them to be established in a well-grounded confidence of their safety, to have good hope for their king, whose countenance was, as it were, a mirror of the merciful and reconciled countenance of God.

The meaning of the words is: Lord, in putting forth your power to sustain and protect the king, you will keep him safe; and, ascribing his safety to your power, he will greatly rejoice in you. The Psalmist has undoubtedly used strength and salvation to mean strong and powerful help; intimating that God's power in defending the king would be such that it would preserve and protect him against all dangers.

In the second verse, the cause of this joy is pointed out. The cause was this: God had heard the prayers of the king and had liberally granted him whatever he desired. It was important for this to be known, and for the faithful to have it deeply impressed on their minds, that all David’s successes were indeed benefits conferred upon him by God and, at the same time, testimonies of his lawful calling.

And David, no doubt, in speaking this way, testifies that he did not give free rein to the desires of the flesh and follow the mere impulse of his appetites. He was not like worldly men, who set their minds on one thing after another without any consideration, just as they are led by their sensual lusts. Instead, David had so bridled his affections as to desire nothing except what was good and lawful.

In accordance with the weakness natural to humankind, he was, it is true, chargeable with some vices, and even fell shamefully on two occasions. However, the general administration of his kingdom was such that it was easy to see that the Holy Spirit presided over it.

But since, by the Spirit of prophecy, the Psalmist was looking principally to Christ (who does not reign for His own advantage, but for ours, and whose desire is directed only to our salvation), we may gather from this the very profitable doctrine that we need have no fear that God will reject our prayers on behalf of the Church. For our heavenly King has gone before us in making intercession for her, so that in praying for her, we are only endeavoring to follow His example.