Create In Me A Clean Heart

He prays for sanctifying grace; and this every true penitent is as earnest for as for pardon and peace. He does not pray, "Lord, preserve me my reputation," as Saul, I have sinned, yet honour me before this people. No; his great concern is to get his corrupt nature changed: the sin he had been guilty of was,
(1.) An evidence of its impurity, and therefore he prays, Create in me a clean heart, O God! He now saw, more than ever, what an unclean heart he had, and sadly laments it, but sees it is not in his own power to amend it, and therefore begs of God (whose prerogative it is to create) that he would create in him a clean heart. He only that made the heart can new-make it; and to his power nothing is impossible. He created the world by the word of his power as the God of nature, and it is by the word of his power as the God of grace that we are clean (Jn. 15:3), that we are sanctified, Jn. 17:17.
(2.) It was the cause of its disorder, and undid much of the good work that had been wrought in him; and therefore he prays, "Lord, renew a right spirit within me; repair the decays of spiritual strength which this sin has been the cause of, and set me to rights again." Renew a constant spirit within me, so some. He had, in this matter, discovered much inconstancy and inconsistency with himself, and therefore he prays, "Lord, fix me for the time to come, that I may never in like manner depart from thee." - Matthew Henry