Psalms 51:10

Create in me a clean heart, O God
Which was now defiled with sin, and of which being convinced, he was led more and more to see the impurity of his heart and nature, from which all his evil actions flowed; and being sensible that he could not make his heart clean himself, and that this was the work of God, and a work which required creating power, he entreats it of him: for as the first work of conversion is no other than a creation, or a production of something new, which was not before; so the restoring of a backslider, as it goes by the same name, it requires the same power; and as the implantation of grace at first, and particularly of faith, is a work of almighty power; so the same power must be put forth to bring it into exercise, after falls into sin; that it may afresh deal with the heart purifying blood of Christ, which only can make it clean, and is what is here meant;

and renew a right spirit within me;
by which is designed, not the Holy Spirit of God ^F11; for he is the renewer; nor the spirit or soul of man as to its essence; but with respect to the qualities of it; and here it signifies a renewing of the inward man, or an increase of grace, and causing it to abound in act and exercise; and intends a spirit of uprightness and integrity, in opposition to dissimulation and hypocrisy; a spirit "prepared [and] ready" ^F12 to every good work, ( Matthew 26:41 ) ; "one firm" ^F13 and unmoved from obedience to the Lord, by sin, temptations, and snares; a heart fixed, trusting in the Lord, and comfortably assured of an interest in pardoning grace and mercy.