John Gill Commentary Psalms 38:20

"They also that render evil for good Are adversaries unto me, because I follow the thing that is good." — Psalms 38:20 (ASV)

They also that render evil for good are mine adversaries
(See Gill on Psalms 35:12);

because I follow [the thing that] good [is] ;
or "follow good"; a good God, whom his soul followed hard after, (Psalms 63:8) ; the good Shepherd of the sheep, who led him into green pastures, whither he followed him, (Psalms 23:1–3) ; the good Spirit of God his guide, whom he walked after, (Romans 8:1) ;

good and holy men of God, whom he took for examples and copied after; and every good work, which he pursued with eagerness and pleasure; and all this drew upon him the hatred of his adversaries.