The Heidelberg Catechism: Lord's Day 27
72. Question: Does this outward washing with water itself wash away sins?
Answer: No, only the blood of Jesus Christ and the Holy Spirit cleanse us from all sins.
 Matt. 3:11; I Pet. 3:21; I John 1:7.
73. Question: Why then does the Holy Spirit call baptism the washing of regeneration and the washing away of sins?
Answer: God speaks in this way for a good reason. He wants to teach us that the blood and Spirit of Christ
remove our sins just as water takes away dirt from the body. But, even more important, He wants to assure us by this divine pledge and sign that we are as truly cleansed from our sins spiritually as we are bodily washed with
 I Cor. 6:11; Rev. 1:5; 7:14.  Mark 16:16; Acts 2:38; Rom. 6:3, 4; Gal. 3:27.
74. Question: Should infants, too, be baptized?
Answer: Yes. Infants as well as adults belong to God's covenant and congregation. Through Christ's blood the redemption from sin and the Holy Spirit, who works faith, are promised to them no less than to adults.
Therefore, by baptism, as sign of the covenant, they must be grafted into the Christian church and distinguished from the children of unbelievers. This was done in the old covenant by circumcision, in place of which baptism was instituted in the new covenant.
 Gen. 17:7; Matt. 19:14.  Ps. 22:11; Is. 44:1-3; Acts 2:38, 39; 16:31.  Acts 10:47; I Cor. 7:14.  Gen.
17:9-14.  Col. 2: 11-13.
The Heidelberg Catechism
Lord's Day 1