Answer: The sacraments or ordinances given by God and instituted by Christ, namely baptism and the Lord’s Supper, are visible signs and seals that we are bound together as a community of faith by his death and resurrection. By our use of them the Holy Spirit more fully declares and seals the promises of the gospel to us.
Scripture: Romans 6:4 – We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
Luke 22:19-20 – And he took bread, and when he had given thanks, he broke it and gave it to them, saying, “This is my body, which is given for you. Do this in remembrance of me.” And likewise the cup after they had eaten, saying, “This cup that is poured out for you is the new covenant in my blood.
Source: New City Catechism