This salutation contains the three elements common in all of Paul"s epistles and other correspondence of his day: the writer, the addressees, and a greeting. [source][source][source]
"This salutation exhibits undoubted resemblances in form to secular letters that have come down to us from the same period. But the differences are greater, and that in three respects. There is the firm assertion of Apostolic authority, the clear indication that those whom he addresses are not ordinary people but a consecrated society, and the spiritual character of the good wishes he sends them." [1][source]