Psalms 18:1

The title gives us the occasion of penning this psalm; we had it before (Sa2 22:1), only here we are told that the psalm was delivered to the chief musician, or precentor, in the temple-songs. Note, The private compositions of good men, designed by them for their own use, may be serviceable to the public, that others may not only borrow light from their candle, but heat from their fire. Examples sometimes teach better than rules. And David is here called the servant of the Lord, as Moses was, not only as every good man is God's servant, but because, with his sceptre, with his sword, and with his pen, he greatly promoted the interests of God's kingdom in Israel. It was more his honour that he was a servant of the Lord than that he was king of a great kingdom; and so he himself accounted it (Psa 116:16): O Lord! truly I am thy servant. In these verses, I. He triumphs in God and his relation to him. The first words of the psalm, I will love thee, O Lord! my strength, are here prefixed as the scope and contents of the whole. Love to God is the first and great commandment of the law, because it is the principle of all our acceptable praise and obedience; and this use we should make of all the mercies God bestows upon us, our hearts should thereby be enlarged in love to him.

— Matthew Henry's Concise Commentary (public domain)