The Didache was written A.D. 70 - 110, and, though not inspired, is a strong witness to the sacramental practice of Christians in the apostolic age. Now friend, the writer and all the readers of that, living somewhere between 70 - 110 AD, all knew Koine Greek... and it's written in Koine Greek... so they likely knew the meaning of words in koine Greek (the language of the NT and the language of the word we are discussing. This extremely popular book (that almost got into the NT Canon) was written perhaps when many of the Apostles were still alive and when there were still eyewitnesses to Christ.... and when people knew and used koine Greek.
In its seventh chapter, the Didache reads, "Concerning baptism, baptize in this manner: Having said all these things beforehand, baptize in the name of the Father and of the Son and of the Holy Spirit in living water [that is, in running water, as in a river]. If there is no living water, baptize in other water; and, if you are not able to use cold water, use warm. If you have neither, pour water three times upon the head in the name of the Father, Son, and Holy Spirit." These instructions were composed either while some of the apostles and disciples were still alive or during the next generation of Christians, and they represent an already established custom.
Now... obviously in the period of 70 - 110 AD, Christians did not understand the situation as was insisted beginning in the 16th Century with the Anabaptists (none of whom spoke koine Greek, few of whom knew it at all). Obviously, they did not understand that the word in question has one and only one meaning: "To physically and entirely immerse in and under water" because he specifically states that it may be by pouring (he PREFERS immersing in living water, but he ALLOWS pouring). And the Didache does NOT insist that we must do it according to the primary meaning of the word or as Jesus was Baptized. Both your points are contradicted by the Didache (written when people knew, understood and used koine Greek)
The testimony of the Didache is seconded by other early Christian writings. Pope Cornelius I wrote that as Novatian was about to die, "he received baptism in the bed where he lay, by pouring" (Letter to Fabius of Antioch [A.D. 251]; cited in Eusebius, Ecclesiastical History, 6:4311).
Cyprian advised that no one should be "disturbed because the people are poured upon or sprinkled when they receive the Lord’s grace" (Letter to a Certain Magnus 69:12 [A.D. 255]). Tertullian described baptism by saying that it is done "with so great simplicity, without pomp, without any considerable novelty of preparation, and finally, without cost, a man is baptized in water, and amid the utterance of some few words, is sprinkled." (On Baptism, 2 [A.D. 203]). Obviously, Tertullian did not consider baptism by immersion the only valid form.
It appears, those that knew and used koine Greek disagree with you. And so did those who lived in the early age of the church. Indeed, it seems all until the 16th Century Anabaptist movement began.
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