7.1 Concerning baptism, baptize thus: [After you have repeated all these
things.] Baptize in the name of the [the Lord]
[cf. 9.5, later changed to ‘Father, Son and Holy Spirit’] in running water.
The text as we have it reads ‘in the name of the Father, Son and Holy Spirit…’ Alan Garrow suggests that this reflects a change, and the original was simply ‘in the name of the Lord.’ Evidence of this is found in 9.5 which retains the original.
DIDACHE scholars and other NT scholars tend to agree that the trinitarian formula, here and in other texts, was probably a scribal emendation during a period of controversy over Christology and the trinity (say, during the time of the Arian controversy, I might suppose).
The Gospel of Matthew parallels this trinitarian baptismal insertion, in the Great Commission (see 28.19).
One further implication of a change like this, would that if the original term was simply ‘the Lord,’ later changed, then this would provide a further bit evidence of the DIDACHE’s early (making it more probably pre-Matthean) with respect to dating and its apostolic authenticity.