Q — “Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit,” [Matthew 28:19].

The fourth century Christian historian Eusebius had access to a library which contained earlier versions of Matthew’s gospel than our present one, which dates from the early fourth century.

Eusebius quoted this passage: “Go ye and make disciples of all the nations in my name, teaching them to observe all things, whatsoever I commanded you.” Nothing about a Trinity.  And Eusebius’ passage is similar to the passage in Mark’s gospel that Matthew used as a source.
Also, in the five reports of baptism in the New Testament, none were said to have been in the name of “the Father and of the Son and of the Holy Ghost” but only in the name of Jesus alone.

Aren’t the two viable explanations that Jesus never gave any command regarding baptizing in the name of the Father, Son, and Holy Ghost or that the early Christians ignored Jesus’s command?

A — An intriguing question, or perhaps better questions and comments! I shall try to answer in some detail, but not necessarily in the order in which the questions/comments have been posed.

The first thing to note is that, while the consensus of scholarship is that Mark was indeed a source of Matthew’s Gospel, that remains a scholarly hypothesis, albeit the most plausible one.

Second, while it is undoubtedly true that Eusebius, the earliest church historian, had access to sources that are no longer available to us, the text of St. Matthew’s gospel that he had is, according to the consensus of scholarship, the text that we now have. You may be thinking about Eusebius quoting the text of Papias (circa 60-130) who said that Matthew composed the oracles of Jesus in “Hebrew” and that the evangelists translated as best they could. Papias probably meant by “Hebrew” the Aramaic language which Jesus and the earliest Christians spoke, but there is not a single shred of evidence of an Aramaic gospel of Matthew. And, of course, the text of Papias that Eusebius had is now lost to us.

Now to the more substantive part of your inquiry, the formula used for baptism in the early church. It seems to be the case, as in fact you note, that many Christian communities baptized “in the name of Jesus.” However, the textual evidence for the Trinitarian baptismal formula in Matthew is almost universal in the earliest papyri (including fragments) and codices of that Gospel. There is really no way to know with historical exactitude Jesus’ words with regard to baptism, but the fact that the Trinitarian formula is used in the Gospel of St. Matthew, which seems to have been the favored gospel in the city of Antioch, the first-century center of Christianity, supports the idea that the Trinitarian formula was used from the earliest times, even if that is not textually evidenced except in St. Matthew. I hope these few remarks are of help.