We are gathered here today to celebrate the sacrament of baptism.

In Reformational theology, baptism is considered a sign and seal. 

Signs in the Bible are mighty works of God. The plagues God put on Egypt are called signs. Jesus’ miracles are called signs. Baptism is called a sign because circumcision was called a sign; circumcision was a sign of God’s promise to bring the seed into the world, something man clearly could not do in his own strength. To call baptism a sign is to confess it is a miracle, every bit as much as the virgin birth of Jesus, every bit as much as the miracles of Jesus performed during his earthly ministry. Baptism is a mighty work of God, judging the fallen flesh and making us a new creation.
What about baptism as a seal? In the Bible a seal is a mark of ownership. Baptism is a seal because in baptism God transfers us from the world to the church, from Adam to Christ, from the kingdom of darkness to the kingdom of light, from the devil’s family to his own family. When you are baptized into the Triune name, you belong to the Trinity and the Trinity belongs to you. You are God’s child; that is the identity baptism seals upon you. Baptism makes your membership in God's family official. This seal is proof and authentication of membership in the covenant.
Of course, with this baptismal sign and seal come certain requirements. The most central requirement is faith. Faith receives and grasps what God offers and bestows in baptism. We trust that even now this little one has faith to receive what God is about to give. In Psalm 22, David says God was his God from the womb; he trusted in God even as a nursing infant. 
These parents desire for their child to be given God’s sign and seal, to be marked as God’s own child and to be brought into his covenant. They want their child to receive all that baptism signifies, and to be sealed with the Spirit as God’s possession.