Here are some things a friend sent me on this:
The Encyclopedia of Religion and Ethics:
As to
Matthew 28:19, it says: It is the central piece of evidence for the traditional (Trinitarian) view. If it were undisputed, this would, of course, be decisive, but its trustworthiness is impugned on grounds of textual criticism, literary criticism and historical criticism. The same Encyclopedia further states that: "The obvious explanation of the silence of the New Testament on the triune name, and the use of another (JESUS NAME) formula in Acts and Paul, is that this other formula was the earlier, and the triune formula is a later addition."
Edmund Schlink, The Doctrine of Baptism, page 28:
"The baptismal command in its
Matthew 28:19 form can not be the historical origin of Christian baptism. At the very least, it must be assumed that the text has been transmitted in a form expanded by the [Catholic] church."
The Tyndale New Testament Commentaries, I, 275:
"It is often affirmed that the words in the name of the Father, and of the Son, and of the Holy Ghost are not the ipsissima verba [exact words] of Jesus, but a later liturgical addition."
Wilhelm Bousset, Kyrios Christianity, page 295:
"The testimony for the wide distribution of the simple baptismal formula [in the Name of Jesus] down into the second century is so overwhelming that even in
Matthew 28:19, the Trinitarian formula was later inserted."
The Catholic Encyclopedia, II, page 263:
"The baptismal formula was changed from the name of Jesus Christ to the words Father, Son, and Holy Spirit by the Catholic Church in the second century."