Jamieson, Fausset and Brown on 2 Corinthians 13:14

14. The benediction which proves the doctrine of the Divine Trinity in unity. "The grace of Christ" comes first, for it is only by it we come to "the love of God" the Father (Joh 14:6). The variety in the order of Persons proves that "in this Trinity none is afore or after other" [Athanasian Creed].

communion--joint fellowship, or participation, in the same Holy Ghost, which joins in one catholic Church, His temple, both Jews and Gentiles. Whoever has "the fellowship of the Holy Ghost," has also "the grace of our Lord Jesus Christ," and "the love of God"; and vice versa. For the three are inseparable, as the three Persons of the Trinity itself [Chrysostom]. The doctrine of the Trinity was not revealed clearly and fully till Christ came, and the whole scheme of our redemption was manifested in Him, and we know the Holy Three in One more in their relations to us (as set forth summarily in this benediction), than in their mutual relations to one another (De 29:29).

Amen--omitted in the oldest manuscripts. Probably added subsequently for the exigencies of public joint worship.