'Sincerity' in the Bible

so that we may keep the feast, not with old leaven, nor with the leaven of evil and wickedness, but with unleavened food of sincerity and truth.

For our glorying is this: the testimony of our conscience, that in simplicity and sincerity of God, not in fleshly wisdom, but in the grace of God, we did conduct ourselves in the world, and more abundantly toward you;

for we are not as the many, adulterating the word of God, but as of sincerity -- but as of God; in the presence of God, in Christ we do speak.