'Sincerity' in the Bible

so that let us celebrate the feast, not with old leaven, nor with leaven of malice and wickedness, but with unleavened bread of sincerity and truth.

For our boasting is this, the testimony of our conscience, that in simplicity and sincerity before God, (not in fleshly wisdom but in God's grace,) we have had our conversation in the world, and more abundantly towards you.

For we do not, as the many, make a trade of the word of God; but as of sincerity, but as of God, before God, we speak in Christ.