Baptism

A sign and seal of union with Christ. Westminster, Belgic and Heidelberg teach infant baptism; the 1689 teaches the baptism of believers.

Therefore go and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit,
Matthew 28:19

Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. This promise belongs to you and your children and to all who are far off—to all whom the Lord our God will call to Himself.”
Acts 2:38–39

Or aren’t you aware that all of us who were baptized into Christ Jesus were baptized into His death? We were therefore buried with Him through baptism into death, in order that, just as Christ was raised from the dead through the glory of the Father, we too may walk in newness of life.
Romans 6:3–4

In Him you were also circumcised, in the putting off of your sinful nature, with the circumcision performed by Christ and not by human hands. And having been buried with Him in baptism, you were raised with Him through your faith in the power of God, who raised Him from the dead.
Colossians 2:11–12

For all of you who were baptized into Christ have clothed yourselves with Christ.
Galatians 3:27

And this water symbolizes the baptism that now saves you also—not the removal of dirt from the body, but the pledge of a clear conscience toward God—through the resurrection of Jesus Christ,
1 Peter 3:21