'Sincerity' in the Bible

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.

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.