Q72. Is then the external baptism with water the washing away of sin itself?
Not at all: for the blood of Jesus Christ only, and the Holy Ghost cleanse us from all sin.
 Matthew 3:11; 1 Peter 3:21; 1 John 1:7; 1 Corinthians 6:11.
Q73. Why then doth the Holy Ghost call baptism “the washing of regeneration,” and “the washing away of sins”?
God speaks thus not without great cause, to-wit, not only thereby to teach us, that as the filth of the body is purged away by water, so our sins are removed by the blood and Spirit of Jesus Christ; but especially that by this divine pledge and sign He may assure us, that we are spiritually cleansed from our sins as really, as we are externally washed with water.
 Revelation 1:5; 1 Corinthians 6:11;  Mark 16:16; Galatians 3:27.
Q74. Are infants also to be baptised?
Yes: for since they, as well as the adult, are included in the covenant and church of God; and since redemption from sin by the blood of Christ, and the Holy Ghost, the author of faith, is promised to them no less than to the adult; they must therefore by baptism, as a sign of the covenant, be also admitted into the Christian church; and be distinguished from the children of unbelievers as was done in the old covenant or testament by circumcision, instead of which baptism is instituted in the new covenant.
 Genesis 17:7; Acts 2:39;  1 Corinthians 7:14; Joel 2:16;  Matthew 19:14;  Luke 1:14–15; Psalm 22:10; Acts 2:39;  Acts 10:47; 1 Corinthians 12:13 and 7:14;  Genesis 17:14;  Colossians 2:11–13.
In our last study we saw that there is close connection (a sacramental union) between water baptism and the inward spiritual reality of regeneration that is pointed to. This doctrine is not a Romish invention as some claim, but really comes from the fact that the Scripture speaks of the sign and the reality in the closest connection. For example, when Ananias met Paul after his Damascus Road conversion experience, he said unto him: “Arise, and be baptised, and wash away thy sins, calling on the name of the Lord” (Acts 22:16). Paul himself would subsequently refer to regeneration as “the washing of regeneration, and renewing of the Holy Ghost” (Tit 3:5), and it appears that when he speaks of baptism, he has in mind both the sign and the reality (see 1 Corinthians 12:13 and Galatians 3:27 for examples).
This leads us to believe with the Reformers that ordinarily every Christian must be baptised, and that outside the visible church there is no ordinary means of salvation. Although God can work without and above means in our salvation, He has ordained the means of grace, and ordinarily, His Holy Spirit communicates grace through the means. That is to say, baptism, as a means of grace, is efficacious only when the Holy Spirit joins the outward sign with the inward grace. In other words, we must not swing to the cultic or Romish position and imagine that it is the act of baptism that saves us or that baptism regenerates us. If it is baptism that saves, then why did Simon Magus (and Judas Iscariot) remained unconverted despite being baptised? Also, what would happen to elect infants dying in infancy before being baptised?
When baptism is received by faith, the child of God is assured that God has really granted inward grace. What about infants of believing parents? We baptise infants because in the Old Testament, the infants of the covenant people of God were circumcised to mark them are being recipients of God’s covenant too (Gen 17:7). In the New Testament, we are God’s covenant people, and the Apostle Peter teaches us: “For the promise is unto you, and to your children…” (Acts 2:39). Therefore as we mark out adult believers from the world with baptism, so we also mark out our children from unbelieving children with baptism, believing that God will make good His promise to save them.
Heidelberg Catechism >