CGW,
Holy Tradition has always taught that we are baptized through immersion. This is seen in the 7th canon of the 2nd Ecumenical Council, which speaks of immersion; in the second homily concerning the performance of mysteries by St. Cyril of Jerusalem, it clearly states: "Ye have confessed the salvific confession, and having immersed yourselves thrice in water, came forth out of it," and in the words of St. Basil the Great: "Through three immersions and the same number of invocations is the great mystery of Baptism performed."
The immersion into water, and specifically a triple immersion, and also a triple coming out of the water was not instituted arbitrarily or accidentally, but as the image of the Resurrection of Christ on the third day. "The water," says blessed Basil, "has the symbolic meaning of death, and accepts the body as into a coffin." How then, do we liken ourselves to the One Who descended into Hades, imitating His burial through baptism? The bodies of those who are baptized in water are buried, in a certain sense. Consequently, baptism mystically represents the laying aside of bodily cares, by the word of the apostle: "In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ" (Col. 2: 11)." St. Cyril, in his commentary on the above words, says: "Thus, with the help of these signs you have represented the three-day burial of Christ because, as our Savior was in the heart of the earth three days and three nights, so in the first coming up from the water you symbolized the first day of His sojourn under the earth, and through your immersion, you symbolized the night. For, as one who walks in the night sees nothing, and he who walks during the day does so in light, so you, having immersed yourself in water saw nothing, as if you saw nothing in the night, and having come forth from the water, you see everything as in daylight. You were both dead and then born. So the salvific water was for you both a coffin and a mother. Although we neither actually die, nor get buried, nor are we nailed to the cross, but only simulate this symbolically, we, however, do indeed achieve salvation. Christ was truly crucified, truly buried, and truly resurrected. He granted all this to us, so that we, in imitating His passions, would become partakers of them and indeed would achieve salvation."
You said:
If "baptizo" simply meant "immersion" then why doesn't the Vulgate translate it so?
So, to simply try and understand the logic (and not that I think you will ever be convinced of anything) I would like to ask, do you believe the different translations of Holy Scripture necessitate us to rethink Holy Tradition?