"And Jesus, when he was baptized, went up straightway out of the water." (Matthew 3: 16).
This shows that He must have gone down into the water. "And John also was baptizing in Aenon near to Salim, because there was much water there." (John 3: 23).
This is also a proof that John baptized by immersion.
The baptism of the eunuch by Philip is described thus in the Bible:
"They went down both into the water, both Philip and the eunuch; and he baptized him. And when they were come up out of the water, the Spirit of the Lord caught away Philip." (Acts 8: 38, 39).
This, again, shows the manner of baptism practiced by the Savior's disciples.
St. Paul writes:
"Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection." (Romans 6: 3, 4, 5).
The apostle here likens baptism to the burial and resurrection of Christ. Any ordinance called baptism performed in some other way is not in the likeness of Christ's death and resurrection, and is not baptism at all.
All the early church historians testify that baptism by immersion was practiced during the first centuries after Christ.