‘For our exhortation is not of error, nor of uncleanness, nor in guile, but even as we have been approved of God to be entrusted with the Good News, so we speak, not as pleasing men, but God who proves our hearts.'
This amplifies the fact that what they preached was God's Good News. Their enemies had clearly charged them with wandering from the truth (as they had accused Jesus of the same), of encouraging immorality (the constant Jewish criticism, usually justified, of pagan religion), and of using guile. So Paul stressed that there was no error in their teaching, no wandering from the truth, there was no lack of morality, there was no deceit or attempts to mislead, rather they spoke as those appointed with the approval of God as worthy proclaimers of that Good News. They preached as those who wanted to please the God Who had appointed them, and Who searched and tested their hearts, and not just to please men. Any pastor or preacher who is of God will follow their example, and should also remember that God will weigh up their message and will test out their inner heart.
‘Approved', that is approved by testing.
‘Not as pleasing men.' The verb often signifies pleasing by service on someone's behalf. So they were God approved, God tested, and intent solely on pleasing God in the way they served.
‘Hearts.' In the Bible this word includes the will and the mind as well as the emotions. It represents the whole of a man's disposition.