'Sincerity' in the Bible

Day by day continuing with one mind in the temple, and breaking bread from house to house, they were taking their meals together with gladness and sincerity of heart,

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

For our proud confidence is this: the testimony of our conscience, that in holiness and godly sincerity, not in fleshly wisdom but in the grace of God, we have conducted ourselves in the world, and especially toward you.

For we are not like many, peddling the word of God, but as from sincerity, but as from God, we speak in Christ in the sight of God.

I am not speaking this as a command, but as proving through the earnestness of others the sincerity of your love also.

Slaves, be obedient to those who are your masters according to the flesh, with fear and trembling, in the sincerity of your heart, as to Christ;

Slaves, in all things obey those who are your masters on earth, not with external service, as those who merely please men, but with sincerity of heart, fearing the Lord.