1) Jesus calls us to it. It is a part of the Great Commission (Mt 28:18-20) and was a common practice of Jesus' followers as people were converted. This continued into the early church.

2) We call it an "ordinance." This means we've been asked to do it, but there is no saving power in the act itself. 

3) It is for believers. Every act of baptism in the Bible is someone who has come to faith in Jesus and wants to pledge their life to Him. We take that seriously, so we only encourage followers of Jesus who believe Him and want to serve Him to take part.

4) It is about association. In the ancient world, baptism was the final step in a transition to being a new person. It did not change what you believed or who you were, but denoted the change you already made or believed in. It was a symbol of association. You were no longer ..., but were now .... In this case, for us, it is a symbol of no longer being dead to sin, but now alive in Christ. Baptism is a public declaration, an ordinance, that shows the belief you already have in Jesus. It does not save you, but is the symbol of the saving you've already received and the commitment you are making to live your life for Him!