In baptism there is a burial, an immersion in water. No other act would so fitly represent the complete ending of a life of sin. If there was no other source of knowledge as to how baptism was performed, this text should settle the matter beyond doubt. There is no burial in sprinkling and pouring a little water on a person's head, but there is a burial in immersion in water. Without going into a lengthy discussion of the subject, we call attention to three lines of evidence, each one independent of the others and each conclusive within itself.
The Lexicons -
Circumstantial Evidence -
John the Baptist baptized the people in the river Jordan (Mark 1:5). If you notice the marginal reading in verse 9, you will see that John baptized Jesus into the Jordan. (See American Standard Version). John could have dipped Jesus into the Jordan, but he could not have sprinkled or poured him into the Jordan. And verse 10 says he came up out of the water. Later "John was baptizing in Ænon near to Salim, because there was much water there" (John 3:23). It does not require much water to sprinkle or pour, but it does require much water to immerse.
When Philip baptized the eunuch, they came to a certain water, they both went down into the water, the baptizing was done while they were in the water, then they came up out of the water (Acts 8:36-
Add to this Paul's statement that we are buried in baptism, and assurance is made doubly sure, even though we did not know the meaning of the Greek word for baptism, nor what the historians, commentators, and critics say.
The New Life -
R. L. Whiteside, Commentary on Romans 6:4