He said not that he “was” a son of Abraham, but that he now is. For before when he was the chief among the publicans, and bore no likeness to the righteous Abraham, he was not his son. But because some murmured that he tarried with a man who was a sinner, he adds in order to restrain them, For the Son of man came to seek and to save that which was lost.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).