Matthew 12:34

“You offspring of vipers, how can you, being evil, speak good things? For out of the abundance of the heart the mouth speaks.”

‘You, being evil.' Jesus was under no illusions about men. He had said a similar thing to His disciples (Matthew 7:11). That did not render them unsavable. Indeed it explained why they needed to be made whole. But the difference was that the Pharisees wanted to go on being evil. And they revealed it continually by what they said. Furthermore by resisting the work of the Holy Spirit they were making themselves even more evil.

For these Pharisees who are so hardened against Him, and are falsely accusing Him (this is not all Pharisees), are revealing their corruptness by their evil words, and confirming it within them. In their subtlety and their reaction to His goodness they are revealing themselves to be like vipers, which lie in the way and bite all who disturb them (compare Genesis 49:17). They are revealing that they are evil. ‘They have sharpened their tongue like a serpent, the poison of vipers is under their lips' (Psalms 140:3). How then can they speak good things? For the mouth speaks what is in the heart. It reveals what is within.