Adam Clarke on Romans 12:7

Or ministry - Διακονια simply means the office of a deacon; and what this office was, see in the note on Act 6:4 (note), where the subject is largely discussed.

Or he that teacheth - The teacher, διδασκαλος, was a person whose office it was to instruct others, who thereby catechizing, or simply explaining the grand truths of Christianity.