1 Thessalonians 2:4
But even as the good news was given to us by the approval of God, so we give it out; not as pleasing men, but God by whom our hearts are tested.
But we all, with unveiled face giving back as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as from the Lord who is the Spirit.
2 Corinthians 3:18
If to others I am not an Apostle, at least I am one to you: for the fact that you are Christians is the sign that I am an Apostle.
1 Corinthians 9:2