John Gill Commentary Psalms 18:39

"For thou hast girded me with strength unto the battle: Thou hast subdued under me those that rose up against me." — Psalms 18:39 (ASV)

For you have girded me with strength for battle
See (Psalms 18:32) ; that natural strength, courage and valour, which David had, were from the Lord; and so is the Spirit of power, love, and of a sound mind, which believers have; and likewise that strength which Christ, as man, had and used in his combat with the powers of darkness; see (Psalms 80:17) ;

you have subdued under me those that rose up against me ;
as the psalmist ascribes his strength, so he attributes his success to the Lord; who likewise subdues the sins of his people, and all other enemies of theirs, and who also makes the enemies of his Son his footstool, (Psalms 110:1) .