There are at least three reasons why every believer should be baptized.  First, they should be baptized to follow the example of Jesus. Matthew 3:16 says, "And after being baptized, Jesus went up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God descending as a dove, and coming upon Him," 

 We know that Jesus never sinned, why do you think John baptized Him?

 In His baptism, Jesus showed us that baptism is important to Him, and gave us an example to follow.  God was pleased at Jesus' baptism and He will be pleased during our’s too.   

 The second reason believers should be baptized is to follow the example of New Testament believers. "So then, those who had received his word were baptized; and there were added that day about three thousand souls. And they were continually devoting themselves to the apostles' teaching and to fellowship, to the breaking of bread and to prayer" Acts 2:41-42 

 On the day of Pentecost, three thousand people made a decision to follow Christ.  The early Church baptized them that very day.  Then the people were faithful to attend Church, fellowship, learn and to pray, but it all began with baptism.

 The third reason believers should be baptized is that God tells us to.

"And Peter said to them, "Repent, and let each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you shall receive the gift of the Holy Spirit."  Acts 2:38 
 Just as the Lord instructs us to repent he tells us to be baptized.  It is not that baptism saves us, rather, it is an announcement of our faith and a symbol of our relationship to Jesus.   The Lord instructed the Church to baptize those who accept Jesus.

 Baptism is the first step of obedience after profession Jesus as our Lord.  And if we are sincere in Him being our Lord, we will not argue with Him when He tells us to do something, we will gladly enter into the water and proudly proclaim to all that He is our Lord!