7 for which I was appointed a preacher and an apostle — I am speaking the truth in Christ and not lying — a teacher of the Gentiles in faith and truth.
appointed = put, placed, appointed to a service (2 Timothy 1:11)
preacher = herald, messenger vested with authority to convey official messages from kings, commanders, etc.
apostle = sent off with credentials and a commission to be an ambassador or envoy (see 1 Timothy 1:1)
I am speaking the truth — Paul had not been appointed an apostle by Christ on earth, nor had he been sent to proclaim the fulfillment of prophecy. Both his apostleship and his message were heavenly in their origin (Galatians 1:11-12), and there were no Scripture passages he could point to in confirmation of his proclamation of “the mystery.” Thus he often speaks under oath, as it were, calling God, or Christ, to witness, both as to his ministry and his message. — Stam, page 60
in Christ — not in the best manuscripts
Gentiles = ethnos = heathen — anyone not Jewish
faith — fidelity, faithfulness (this is probably the meaning in this context, although it can also refer to the act of trusting or to the object of the faith)
I think the full scope of this passage (going back to the beginning of chapter 2) is easy to miss. Paul is stating that ALL men — Jews and Gentiles — can be saved through Christ, who gave Himself for ALL. But God didn’t proclaim this message until the proper time — the “due time” when God wanted the message told. And it was for THIS reason (to tell the message that all could be saved through Christ) that Paul was appointed an ambassador. This is one of many occasions in Paul’s writings where he states unequivocally that he was saying something new that nobody else had said — that God had given him a different message than what had been proclaimed up until this time. That message is that ALL could be saved by faith alone in Christ alone, apart from the law, apart from works apart from the Old Testament religion.