Let us notice also how he thinks to cast discredit upon our system of morals, alleging that it is only common to us with other philosophers, and no venerable or new branch of instruction. In reply to which we have to say, that unless all men had naturally impressed upon their minds sound ideas of morality, the doctrine of the punishment of sinners would have been excluded by those who bring upon themselves the righteous judgments of God. It is not therefore matter of surprise that the same God should have sown in the hearts of all men those truths which He taught by the prophets and the Saviour, in order that at the divine judgment every man may be without excuse, having the “requirements of the law written upon his heart,”— a truth obscurely alluded to by the Bible in what the Greeks regard as a myth, where it represents God as having with His own finger written down the commandments, and given them to Moses, and which the wickedness of the worshippers of the calf made him break in pieces, as if the flood of wickedness, so to speak, had swept them away.
But Moses having again hewn tables of stone, God wrote the commandments a second time, and gave them to him; the prophetic word preparing the soul, as it were, after the first transgression, for the writing of God a second time.
Source: Against Celsus (New Advent)