I have not had much sleep the last two days, so will find a commentary that expresses my belief of what this means. See Psalm 41:2 for example.
Barnes commentary:
" acts of piety will be partially rewarded on the earth; or that the divine favor will be shown to those who deal kindly with others. This principle is often referred to in the Scriptures. See
Psalm 1:3, note;
Psalm 37:3-4, note;
Psalm 37:11, note;
Psalm 37:23-26, note;
Psalm 37:37, note; compare
Matthew 5:5;
1 Timothy 4:8. The par ticular application here is, that if any one showed kindness to him that was sick or enfeebled by disease, he might expect that God would interpose in his case under similar circumstances, and would "preserve" him, or "keep him alive."
It is not to be interpreted as teaching that this would be universally true, or that he who did this would never die, but the meaning is, that he might look for special divine aid and favor, when he in turn should be sick."
And he shall be blessed upon the earth - This is in accordance with the doctrine noticed above, and so often referred to in the Psalms and elsewhere, that the effect of religion will be to promote happiness and prosperity in this life."