“This is what the gospel is: a series of promises expressed in words. God promises forgiveness, acquittal, adoption, preservation, resurrection, and glory. The sacraments are like the signature at the bottom of the contract. In the past, agreements weren’t signed; they were sealed with a wax impression. So the Reformers spoke of the sacraments as seals. But today a signature is our normal way of confirming commitments.
The covenant Promises God makes to us in the gospel are signed and sealed with water, bread, and wine. The signature doesn’t add any new content to the promises; nor does it enact them. But it does seal and confirm those promises. Without a signed contract you might still have reason to be optimistic that someone would fulfill his or her promises, but a signature gives you much greater confidence. You have something you can point to, a commitment you can hold in your hand. And God has graciously given us baptism and Communion to give us greater confidence in his promises.”