Albert Barnes Commentary Psalms 18:1

"I love thee, O Jehovah, my strength." — Psalms 18:1 (ASV)

I will love thee, O Lord - This verse is not found in the song in 2 Samuel 22. It appears to have been added after the first composition of the psalm. This addition could have been made either by David, as an expression of his ardent love for the Lord in view of His merciful interventions on his behalf and upon the most careful and mature review of those mercies.

Alternatively, it may have been added by the collector of the Psalms when they were adapted for public worship, serving as a proper commencement for the psalm—expressive of the feeling that the general tenor of the psalm was suited to inspire.

It is impossible now to determine by whom it was added, but no one can doubt that it is a proper commencement for a psalm designed to recount so many mercies. It is the feeling that all should have when they recall the goodness of God to them in their past lives.

My strength - This refers to the source of my strength, or the One from whom all my strength is derived. So, in Psalms 27:1, it says, “The Lord is the strength of my life.” In Psalms 28:8, “he is the saving strength of his anointed.” Compare Psalms 29:11; Psalms 46:1; Psalms 73:26; Psalms 81:1; Psalms 140:7.