John 1:25 KJV
And they asked him, and said unto him, Why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet?
When asked why he baptized, John the Baptist gave two clear responses;
• He baptized to make Christ manifest to Israel. (vs 31)
• He baptized because he was sent to baptize (vs 33).
These two reasons suffice even today: we baptize to make Christ and faith in Christ public and we baptize (and are baptized) out of shear obedience.
We baptize because we are taught to do so in the Word of God. The context of the passage puts all of the emphasis upon Christ and not upon the one baptizing or the ones being baptized. Keep Christ lifted up!