Albert Barnes 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 who return evil for good - They whose characteristic it is to return evil for good, are opposed to me. This implies that those who were now seeking his ruin had formerly been benefited by him. They were persons who cherished no grateful recollection of favors bestowed on them, but who found a pleasure in persecuting and wronging their benefactor. Compare Psalms 35:12-16. “Are my adversaries.” Are now opposed to me; have become my enemies.

Because I follow what is good - This properly means, Because I follow the good. The Hebrew word translated “because” - תחת tachath - properly means the lower part; what is underneath; then below; and beneath. The idea here is that the “underlying reason” for what they did was that he followed good, or that he was a righteous man; or, as we say, this was “at the bottom” of all their dealings with him.

Sinner as he felt he was (and as he acknowledged he was) before God, and true as it was that his “sickness” was brought upon him by God for his sinfulness, yet the reason “men” treated him as they did was that he was a friend of God - a religious man. Their conduct, therefore, was sheer persecution.

We may, with entire consistency, be very humble before God, and acknowledge that we deserve all that He brings upon us; and yet, at the same time, we may be aware that we have not wronged men, and that their conduct toward us is wholly undeserved, is most ungrateful, and is sheer malignity against us.