'Sincere' in the Bible

Give sincere homage to the Son, lest he be angry, and you perish in the way, for his wrath will soon be kindled. Blessed are all those who take refuge in him. A Psalm by David, when he fled from Absalom his son.

in pureness, in knowledge, in patience, in kindness, in the Holy Spirit, in sincere love,

so that you may approve the things that are excellent; that you may be sincere and without offense to the day of Christ;

but the goal of this command is love, out of a pure heart and a good conscience and sincere faith;

having been reminded of the sincere faith that is in you; which lived first in your grandmother Lois, and your mother Eunice, and, I am persuaded, in you also.

Seeing you have purified your souls in your obedience to the truth through the Spirit in sincere brotherly affection, love one another from the heart fervently:

This is now, beloved, the second letter that I have written to you; and in both of them I stir up your sincere mind by reminding you;