John Gill Commentary Psalms 31:16

"Make thy face to shine upon thy servant: Save me in thy lovingkindness." — Psalms 31:16 (ASV)

Make your face to shine upon your servant
In which he prays for the gracious presence of God, the manifestations of himself unto him, the discoveries of his love, the enjoyment of him in Christ, communion with him, the comforts of his Spirit, and joys of his salvation; see (Numbers 6:25Numbers 6:26) ;

save me for your mercies' sake ;
not for any merit and righteousness of his own, but for the sake of the grace and goodness of the Lord; which is putting salvation, whether temporal or spiritual, upon its right foot and foundation; which is never wrought out by, or is for works of righteousness done by men, but according to the grace and mercy of God.