Create in me a clean heart, O God - 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 Genesis 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. This, he felt, could be produced only by the power of God; and the passage, therefore, proves that it is a doctrine of the Old Testament, as it is of the New, that the human heart is changed only by a divine agency.
And renew a right spirit within me - Margin, “a constant spirit.” The Hebrew word - נכון nākûn - means properly, that which is “erect,” or that which is made to stand up, or which is firm or established. It is used to denote
(a) that which is upright, right, proper: Exodus 8:26; Job 42:8; Psalms 5:9;
(b) that which is right, true, sincere, Psalms 78:37;
(c) that which is firm, constant, fixed.
This would seem to be the meaning here. He prays for a heart that would be firm in the purposes of virtue; that would not yield to temptation; that would carry out holy resolutions; that would be stedfast in the service of God. The word “renew” here means to be or to make new; to produce something new. It is also used in the sense of making anew, as applied to buildings or cities in the sense of “rebuilding” or “repairing” them: Isaiah 61:4; 2Ch 15:8; 2 Chronicles 24:4. The word here would naturally convey the idea that there had been formerly a right and proper spirit in him, which he prayed might now be restored. The language is that of one who had done right formerly, but who had fallen into sin, and who desired that he might be brought back into his former condition.