A.T. Robertson Commentary Matthew 3:9

"and think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham." — Matthew 3:9 (ASV)

And think not to say within yourselves (κα μη δοξητε λεγειν εν εαυτοις). John touched the tender spot, their ecclesiastical pride. They felt that the "merits of the fathers," especially of Abraham, were enough for all Israelites. At once John made clear that, reformer as he was, a breach existed between him and the religious leaders of the time.

Of these stones (εκ των λιθων τουτων). "Pointing, as he spoke to the pebbles on the beach of the Jordan" (Vincent).