Create in me a clean heart, O God,
& renew a steadfast spirit within me.
I will give you a new heart and put a new spirit in you;
I will remove from you your heart of stone and give you a heart of flesh.
A new heart - A new frame of soul, a mind changed, from sinful to holy, from carnal to spiritual. A heart in which the law of God is written, Jer 31:33.
A sanctified heart, in which the almighty grace of God is victorious, and turns it from all sin to God.
A new spirit - A new, holy frame in the spirit of man; which is given to him, not wrought by his own power.
The stony - The senseless unfeeling.
Out of your flesh - Out of you. Of flesh - That is, quite of another temper, hearkening to God's law, trembling at his threats, moulded into a compliance with his whole will; to forbear, do, be, or suffer what God will, receiving the impress of God, as soft wax receives the impress of the seal.
~ John Wesley
new heart-mind and will.
spirit-motive and principle of action.
stony heart-unimpressible in serious things; like the "stony ground" (Mt 13:5, 20), unfit for receiving the good seed so as to bring forth fruit.
heart of flesh-not "carnal" in opposition to "spiritual"; but impressible and docile, fit for receiving the good seed. In Eze 18:31 they are commanded, "Make you a new heart, and a new spirit." Here God says, "A new heart will I give you, and a new spirit will I put within you." Thus the responsibility of man, and the sovereign grace of God, are shown to be coexistent. Man cannot make himself a new heart unless God gives it (Php 2:12, 13).
~ Jamieson-Fausset-Brown Bible Commentary
Water is an emblem of the cleansing our polluted souls from sin. But no water can do more than take away the filth of the flesh. Water seems in general the sacramental sign of the sanctifying influences of the Holy Ghost; yet this is always connected with the atoning blood of Christ. When the latter is applied by faith to the conscience, to cleanse it from evil works, the former is always applied to the powers of the soul, to purify it from the pollution of sin. All that have an interest in the new covenant, have a new heart and a new spirit, in order to their walking in newness of life. God would give a heart of flesh, a soft and tender heart, complying with his holy will. Renewing grace works as great a change in the soul, as the turning a dead stone into living flesh. God will put his Spirit within, as a Teacher, Guide, and Sanctifier. The promise of God's grace to fit us for our duty, should quicken our constant care and endeavour to do our duty. These are promises to be pleaded by, and will be fulfilled to, all true believers in every age.
~ Matthew Henry