Heidelberg Catechism · 1563

Q73. Why then does the Holy Spirit call baptism the washing of regeneration and the washing away of sins?

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 water.
Answer · Heidelberg Catechism

Scripture proofs

  1. [1]
    1 Corinthians 6:11

    And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.

    Revelation 1:5

    And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood,

    Revelation 7:14

    And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.

  2. [2]
    Mark 16:16

    He that believeth and is baptized shall be saved; but he that believeth not shall be damned.

    Acts 2:38

    Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.

    Romans 6:3-4

    Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death? Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.

    Galatians 3:27

    For as many of you as have been baptized into Christ have put on Christ.

Proof texts as given in the original; verse text from the King James Version.