What is Baptism & Who is it For?
What is Baptism?
Baptism is one of two Sacraments in the New Testament. We do not often use the word Sacrament as evangelicals, so let me provide a definition. A Sacrament is a holy ordinance instituted by Christ; wherein, by sensible signs, Christ, and the benefits of the new covenant
[i.e. salvation], are represented, sealed, and applied to believers (Westminster Shorter Catechism Question 92).  The Sacraments are visible displays of God’s love, and by the power of the Holy Spirit, they apply Jesus Christ and all of his benefits to us.
In Baptism, the washing with water in the name of the Father, Son, and Holy Spirit, signifies and seals our ingrafting into Jesus Christ, our partaking in the benefits of salvation, and our engagement to be the Lord’s (See Westminster Shorter Catechism question 94). Insofar as Baptism signifies these things, it visibly represents our union with Jesus Christ, and the washing away of our sins. Baptism (like circumcision before it) is a seal of the righteousness that is by faith (Romans 4:11). As a seal, baptism is meant to confirm our faith and to certify the reality of God’s saving work in us.
John Calvin (1509-1564) wrote,
“The seals which are attached to government documents and other public acts are nothing taken by themselves, for they would be attached in vain if the parchment had nothing written on it. Yet when added to the writing, they do not on that account fail to confirm and seal what is written.” (Institutes IV.XIV.5)
In this same way Baptism serves as a “seal” for our benefit, confirming the reality of God’s gracious promises to us. In Baptism those promises include regeneration, union with Christ in his death and resurrection, union with the church, and the washing away of our sins. These promises are truly conveyed in the Sacrament, and apprehended by us through the Spirit’s work of faith in our hearts. Baptism is primarily about God’s action, since these realities are wrought by Him. In a secondary sense we may identify baptism as our confession, but it’s our confession in response to God’s action. They are His gracious promises, and it is His Spirit at work in us.
As a Sacrament, Baptism is also the Sacrament of initiation. It is the door into the visible church for both infants, and adults. A person who is not baptized has not technically entered into what it means to be a disciple of Jesus. In fact, when Jesus described the formula for making disciples in Matthew 28:19-20, he said that first came “baptizing.” This makes sense when we consider that one of the things signified in baptism is being born again (John 3:3-5). Birth is our initiation into a new world, and in one sense that’s what baptism is too!
 If the word “Sacrament” bothers you because you haven’t read it in the Bible, consider this: the substance of the word “Sacrament” is in Scripture, just like the substance of the word “Trinity” is in Scripture. Words like Sacrament, or Trinity, may not appear in Scripture (as do words like grace, and sin), but what they describe does. Therefore, the word Sacrament serves to convey the reality of what the Bible teaches, i.e. that God by the power of His Spirit is mysteriously working in our lives through physical means like water, bread, and wine. In fact, the word Sacrament is just a translation of the Greek word for mystery!