Psalms 18:20-24

As God had promised to bless those of His people who walked in obedience to His will (Deuteronomy 28), so he blessed David who followed the Lord faithfully. By recounting his own righteousness David was not implying that he merited God’s favor simply because of his good works. He was showing God’s faithfulness to His covenant promises to Israel. These verses would have encouraged the Israelites to follow David’s example of righteous behavior so they, too, would experience God’s favor (cf. 2 Timothy 4:6-8).

". . . David could quite properly use this language within a limited frame of reference, [but] the Messiah could use it absolutely; and the psalm is ultimately Messianic . . ." [Note: Kidner, p. 93.]