To be insincere/ twofaced/ hypocritical/ smooth tongue, black heart

To speak words one does not intend; to say one thing but mean another. To put on a façade. 'His mouth and his heart were not equal.'

('Three does the Holy One, blessed be He, hate: one who speaks one thing with the mouth and another with the heart...' - Pesachim 113b), and also: 'And they could not speak peace; from their disgrace we learned their praise, that they did not speak one thing with the mouth and another with the heart' - Rashi on Genesis 37:4, and also: 'It is forbidden for a person to conduct himself with words of division and enticement, and not be one thing in the heart and another, but his inside shall be as his outside, and the matter in the heart is the thing spoken with the mouth' - Rambam, Sefer Hamada, Hilchot De'ot 6:99, and also: 'The Holy One, blessed be He, hates this man who speaks one thing with the mouth and another with the heart' - Rabbi Nachman of Breslov, Sefer Hamidot, Emunah, and also: 'Much cunning and deceit in the world. Falsehood and truth meet... one thing they speak with the mouth and another with the heart' - Burla, Alilot Akavya, 189)

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