Luke 3:7-9 (NKJV)
Then he said to the multitudes that came out to be baptized by him, "Brood of vipers! Who warned you to flee from the wrath to come? Therefore bear fruits worthy of repentance, and do not begin to say to yourselves, 'We have Abraham as our father.' For I say to you that God is able to raise up children to Abraham from these stones. And even now the ax is laid to the root of the trees. Therefore every tree which does not bear good fruit is cut down and thrown into the fire."
John the Baptist did not mind speaking the plain truth. He was not out to win friends, but he certainly did influence his enemies.
This is the period of time in which God puts Israel aside because of their unfruitfulness, and begins the age of grace based on the work of Christ on the cross. The ax was laid to the root of the tree about to be cut down. But even though God has laid Israel aside at this point, He is not through with them yet. There is a day coming in which the believing remnant of Israel will be raised up.
Romans 11:25-27 (NKJV)
For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in. And so all Israel will be saved, as it is written: "The Deliverer will come out of Zion, And He will turn away ungodliness from Jacob; For this is My covenant with them, When I take away their sins."