Whereunto I am appointed a preacher, and an apostle, and a teacher of the Gentiles. Whereunto I am appointed a preacher - Κηρυξ, a herald. See the notes at Matthew 3:17.
And an apostle - Sent immediately from God to man.
A teacher - One whose business it is to instruct men, and particularly the Gentiles, to whom he was especially sent; to proclaim the doctrines of eternal life, the resurrection and final incorruptibility of the human body; and, in a word, the salvation both of the body and soul of man by Christ Jesus.