Here is some very fine commentary on this text from two men you probably are familiar with....
The word rendered “create,” ברא berâ' - is a word which is properly employed to denote an act of “creation;” that is, of causing something to exist where there was nothing before. It is the word which is used in Gen_1:1 : “In the beginning God “created” the heaven and the earth,” and which is commonly used to express the act of creation. It is used “here” evidently in the sense of causing that to exist which did not exist before; and there is clearly a recognition of the divine “power,” or a feeling on the part of David that this could be done by God alone. The idea is, however, not that a new “substance” might be brought into being to which the name “a clean heart” might be given, but that he might “have” a clean heart; that his heart might be made pure; that his affections and feelings might be made right; that he might have what he was conscious that he did “not” now possess - a clean or a pure heart. - Albert Barnes
“Create.” What! has sin so destroyed us, that the Creator must be called in again? What ruin then doth evil work among mankind! “Create in me.” I, in outward fabric, still exist; but I am empty, desert, void. Come, then, and let thy power be seen in a new creation within my old fallen self. Thou didst make a man in the world at first; Lord, make a new man in me! “A clean heart.” In the seventh verse he asked to be clean; now he seeks a heart suitable to that cleanliness; but he does not say, “Make my old heart clean;” he is too experienced in the hopelessness of the old nature. He would have the old man buried as a dead thing, and a new creation brought in to fill its place. None but God can create either a new heart or a new earth. Salvation is a marvellous display of supreme power; the work in us as much as that for us is wholly of Omnipotence. The affections must be rectified first, or all our nature will go amiss. The heart is the rudder of the soul, and till the Lord take it in hand we steer in a false and foul way. O Lord, thou who didst once make me, be pleased to new make me, and in my most secret parts renew me.
“Renew a right spirit within me.” It was there once, Lord, put it there again. The law on my heart has become like an inscription hard to read: new write it, gracious Maker. Remove the evil as I have entreated thee; but, O replace it with good, lest into my swept, empty, and garnished heart, from which the devil has gone out for awhile, seven other spirits more wicked than the first should enter and dwell. The two sentences make a complete prayer. “Create” what is not there at all; “renew” that which is there, but in a sadly feeble state. - C.H. Spurgeon