There is next to be answered the following query: “And how is it that he repents when men become ungrateful and wicked; and finds fault with his own handwork, and hates, and threatens, and destroys his own offspring?” Now Celsus here calumniates and falsities what is written in the book of Genesis to the following effect: “And the Lord God, seeing that the wickedness of men upon the earth was increasing, and that every one in his heart carefully meditated to do evil continually, was grieved He had made man upon the earth.
And God meditated in His heart, and said, I will destroy man, whom I have made, from the face of the earth, both man and beast, and creeping thing, and fowl of the air, because I am grieved that I made them;” quoting words which are not written in Scripture, as if they conveyed the meaning of what was actually written. For there is no mention in these words of the repentance of God, nor of His blaming and hating His own handwork. And if there is the appearance of God threatening the catastrophe of the deluge, and thus destroying His own children in it, we have to answer that, as the soul of man is immortal, the supposed threatening has for its object the conversion of the hearers, while the destruction of men by the flood is a purification of the earth, as certain among the Greek philosophers of no mean repute have indicated by the expression: “When the gods purify the earth.” And with respect to the transference to God of those anthropopathic phrases, some remarks have been already made by us in the preceding pages.
Source: Against Celsus (New Advent)