There are two sacraments or ordinances. There’s baptism, which is once for all. And there’s the Lord’s Supper, which is ongoing and regular. We call both of them ordinances because Jesus Christ commands us to do them. But we call them sacraments because through them God’s blessing and grace come to us in unique ways. They are not just personal, individual experiences. We are members of a community, and baptism and the Lord’s Supper show that we belong to that community, the covenant community, the people who belong to Jesus. And that’s the reason why these are actually like boundary markers. The Westminster Confession says they “put a visible difference between those that belong to the church and the rest of the world.”
They are both signs and seals. We call them signs because they symbolize the blessings of salvation, forgiveness for sins, reception of the Holy Spirit, and the ability to commune with Jesus Christ in his presence. But they’re not only signs; they’re also seals. That means they actually bring these blessings to us. They assure us and stir up our faith, and it’s our faith that receives those blessings.
Some places in the Bible, such as 1 Corinthians 10 and 1 Peter 3, seem to say that it’s the sacraments that actually receive the blessings of salvation. But the sacraments stir up our faith, and our faith is what actually receives the blessings and what saves us. So J. I. Packer puts it like this: “As the preaching of the Word makes the gospel audible, so the sacraments make it visible, and God stirs up faith by both means.” Sacraments, therefore, function as a means of grace on the principle that, literally, seeing leads to believing.