Bible Verses About Sincerity: Servants must render honest service

Servants, be obedient to them that are your lords according to the flesh, with fear and trembling, in the simplicity of your heart, as to Christ.

Not serving to the eye, as it were pleasing men: but, as the servants of Christ, doing the will of God from the heart.

With a good will serving, as to the Lord, and not to men.