This may give you an idea of how Baptists justify their position:
baptistdistinctives.org
Although some early Baptists baptized by pouring or sprinkling water over a person, Baptists concluded that immersion of a person’s entire body in water was the only biblical way to baptize. Therefore, in spite of persecution, inconvenience and ridicule, they began to practice baptism only by immersion. Today, that is the Baptist way throughout most of the world.
The belief in immersion as the proper mode of baptism is based on the Bible for several reasons:
– The English word “baptize” comes from a word in the Greek language—the language in which the New Testament originally was written—that means “to dip, submerge, or immerse.”
– John the Baptist baptized Jesus in the Jordan River by immersion as Jesus began his public ministry (Matthew 3:13-17; Mark 1:9-11).
– Christ’s disciples in New Testament times baptized by immersion (Acts 8:36-39).
– Immersion is a means not only of declaring that Christ died, was buried and was resurrected to provide salvation but also of testifying about our own hope of resurrection (Romans 6:5).
– The New Testament teaches that immersion is a way to symbolize that a believer has died to an old way and is alive to walk a new way in Christ (Romans 6:3-4; Colossians 2:11-12).