The word baptize comes from the Greek word “baptizo” and literally means, “to dip, to immerse, to plunge.” In addition to the literal meaning of the word, immersion is practiced because it was the practice of the church in apostolic times. Still further, only immersion conforms to the description of baptisms as given by the apostle Paul in Romans 6:3-5 where he speaks of it as a burial and resurrection.

Romans 6:3-5

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.