Father,
. . . Son, . . . Holy Spirit. If we approach this verse with a fully developed post-Nicene
orthodoxy in our minds, we shall be just as unsympathetic to our sources as are
those who find in this verse a highly sophisticated and much later stage of
doctrinal formulation retrojected into the text. For all we know, such a saying
may have stood in the now-lost ending of Mark. Even apart from such
speculation, the concept of God as Father, Son, and Holy Spirit is clearly as
old as the Messianic Community as it is known to us in the New Testament. Cf.,
for example, I Cor xii 4-6; II Cor xiii 14; I Peter i 2; I John iii 23-24. In Mark we have “Father” and “Son” so obviously antithetical that—allowing for
Jewish beliefs about “the Spirit”—it plainly opened the way to trinitarian
belief. The antithesis Father-Son is found in Matt xvi 27 and is very common in
John. But what is also common in John is the emphasis on the Paraclete, clearly
represented as being neither Father nor Son. (W.
F. Albright and C. S. Mann, Matthew: Introduction, Translation, and Notes [AB
26; New York: Doubleday, 1971], 362)