Paul, Silvanus, and Timothy, to the assembly of the Thessalonians in God the Father and the Lord Jesus Christ: Grace to you and peace from God our Father and the Lord Jesus Christ.
All letters and other written communications, in NT times, were written upon parchments and conveyed to their recipients in rolled-up form; and that ancient style of letter required, as a practical consideration, that the signature of the writer be at the beginning. Otherwise, it would have been necessary to unroll the entire scroll to find the name of the sender. Therefore, Paul followed the custom of the times in placing his name along with the salutation in the beginning of the epistle (1).