'Insincerity' in the Bible

The same is true of you: outwardly you seem to the human eye to be good and honest men, but, within, you are full of insincerity and disregard of God's Law.

and above all make your own life a pattern of right conduct, having in your teaching no taint of insincerity, but a serious tone,

The wisdom from above is first of all pure, then peaceful, courteous, not self-willed, full of compassion and kind actions, free from favouritism and from all insincerity.

Rid yourselves therefore of all ill-will and all deceitfulness, of insincerity and envy, and of all evil speaking.