In many ways, the ordinance of water-baptism is like a wedding ring - it is an outward expression of an inner, invisible commitment.
Just as a wedding ring doesn't make someone married, water-baptism doesn't bring anyone into right standing with Jesus.
And just as a married person intentionally NOT wearing his/her wedding ring would cause others to raise questions and voice concerns, so too does a believer who intentionally neglects Jesus' command to be baptized cause his/her relationship with the Lord to come into question in the eyes of others...
Baptism is:
A Command (Matthew 28:18-20)
A Sign (Romans 6:1-11)
A Statement of Intent (Romans 6:12-14)