'Sincerity' in the Bible

For our rejoicing is this, the testimony of our conscience, that in simplicity and godly sincerity, not with fleshly wisdom, but by the grace of God, we have had our conversation in the world, and more abundantly to you-ward.

For we are not as many, which corrupt the word of God: but as of sincerity, but as of God, in the sight of God speak we in Christ.

We are not again commending ourselves to your favour, but are furnishing you with a ground of boasting on our behalf, so that you may have a reply ready for those with whom superficial appearances are everything and sincerity of heart counts for nothing.

I speak not by commandment, but by occasion of the forwardness of others, and to prove the sincerity of your love.

But I am afraid lest somehow, as the serpent deceived Eve by his craftiness, your minds may be led astray from the sincerity and the purity of [devotion] to Christ.

And our prayer to God is that you may do nothing wrong; not in order that our sincerity may be demonstrated, but that you may do what is right, even though our sincerity may seem to be doubtful.