First of all, Eusebius was not a Trinitarian; he was an Arian.
In fact, Eusebius of Caesarea had written a letter to Alexander, the bishop who excommunicated Arius, demanding he restore Arius.
He who is being baptized shall say accordingly: I believe, and so he is baptized a third time.”“…But if any one objects, by way of saying that Novatian holds the same law which the universal church holds, baptizes with the same symbol with which we baptize, knows the same God and Father, the same Christ the Son, the same Holy Spirit, and that for this reason he may claim the power of baptizing, namely, that he seems not to differ from us in the baptismal interrogatory; let any one that thinks that this may be objected, know first of all, that there is not one law of the creed…” The traditional reading of Matthew 28.19 was alive and well before a.d. Furthermore, I have not found any controversy over the authenticity of this text anywhere.
This is mounting up to be a really solid case: not only do ALL extant Greek manuscripts with Matthew 28.19 in them contain the traditional reading, but all of the church fathers in the second and third century that quote or allude to it use the traditional version.
Although it certainly wouldn’t ruin my day if Matthew 28.19 turned out to be spurious, I am wary of textual arguments motivated by theology.
It reads, “Therefore, go, teach all nations, baptizing them in the name of the father and of the son and of the holy spirit” (Mat 28.19).Early Quotes by Christian Authors Even if we cannot find or access early manuscripts before the fourth century to see if they contain Matthew 28.19, we can still consult the many Christian authors who lived in the second and third centuries to see how they cited it. Give public instruction on all these points, and then baptize in running water, in the name of the Father and of the Son and of the Holy Spirit.If you do not have running water, batpize in some other. If you have neither, then pour water on the head three times in the name of the Father, Son, and Holy Spirit.Eusebius of Caesarea The theory goes that Eusebius quoted a shortened version of Matthew 28.19 before the council of Nicea in a.d.325 and then quoted the longer, more Trinitarian, version thereafter.