Scripture teaches that mankind was made to know and love God. However, all of mankind has sinned and broken their relationship with God. Because God is Holy, he cannot tolerate sin in His presence. No human effort, including baptism, can compensate or make right our sinfulness.

But God, demonstrating both His justice and His love, has paid sin’s penalty by sending His only son, Jesus Christ, who lived the life we couldn't, died the death we deserved on the cross, and rose again to give us new life. When we place faith in Jesus Christ, we receive God’s gift of forgiveness and new life in Christ as He restores our us to a right relationship with Him.

Baptism is a public testimony that richly symbolizes these spiritual truths. Our descent into the water visualizes our death to sin and our emergence from the water proclaims our new life in Christ. Baptism is simply a public declaration that we now identify with the death, burial, and resurrection of Christ.

"Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life. For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection."
 (Romans 6:3-5, NKJV)

Since baptism is a public profession of faith in Jesus Christ, it should be performed after one understands the Gospel, experiences God’s grace, and responds to it through faith in Jesus Christ. Baptism performed prior to these three things is representative of something other than new life in Christ and falls short of what Jesus calls us to. Many who were baptized as infants need not feel offended by this biblical understanding of baptism, for their infant baptism was performed out of the best intentions. However, obedience to Jesus’ teachings on His terms requires that baptism be representative of faith in Him, therefore it must be done after one is saved.  Baptism is the first step of obedience in our relationship with Christ.

And he brought them out and said, “Sirs, what must I do to be saved?” So they said, “Believe on the Lord Jesus Christ, and you will be saved, you and your household.” Then they spoke the word of the Lord to him and to all who were in his house. And he took them the same hour of the night and washed their stripes. And immediately he and all his family were baptized. Now when he had brought them into his house, he set food before them; and he rejoiced, having believed in God with all his household.
(Acts 16:30-34, NKJV)

Our English word “baptize” originates from the Greek word “baptizo”, which quite literally means “full immersion”. Proper biblical baptism requires full immersion in water, rather than sprinkling or partial immersion. Our death to sin’s control and new lives in Christ are symbolically portrayed as we descend into and emerge from the baptism waters.

Now John also was baptizing in Aenon near Salim, because there was much water there. And they came and were baptized. (John 3:23 NKJV)

Since baptism is a public profession of a Christian’s personal faith and belief in Jesus Christ’s sacrifice on our behalf, only those who have professed faith in Jesus Christ as Lord and Savior should be baptized (this is known as Believers Baptism).

For you are all sons of God through faith in Christ Jesus. For as many of you as were baptized into Christ have put on Christ.(Galatians 3:26-27, NKJV)

The main reason Christians should get baptized is because Jesus calls for it in scripture. Jesus calls for baptism for a very good reason too. The very essence of baptism is inseparable from our faith in Christ as it provides a rich explanation of God’s work in the life of the new believer.

Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, (Matthew 28:19, NKJV)