Baptism as Assurance for the Faithful
Finally, the Reformed position is that as a sign and seal, baptism (as well as the Lord’s supper) serves as confirmation and assurance of God’s blessing (through Christ’s work) to each of us personally. This is because we receive the sign onto (or into) our own bodies. Because we are human beings, and live in physical bodies, we can be strongly influenced by physical, tangible realities that we experience with our external senses. Consider the example of child training through spanking.
Proverbs 22:15 Foolishness is bound up in the heart of a child; The rod of discipline will remove it far from him.
Although the foolishness is an internal problem (that manifests itself externally!), it is actions on the outside of the body that remove it (through the power of the Spirit). The Belgic Confession, in Article 33, paragraphs 1 & 2, states of the sacraments:
We believe that our good God, mindful of our crudeness and weakness, has ordained sacraments for us to seal his promises in us, to pledge his good will and grace toward us, and also to nourish and sustain our faith.
He has added these to the Word of the gospel to represent better to our external senses both what he enables us to understand by his Word and what he does inwardly in our hearts, confirming in us the salvation he imparts to us.
As the confession states, in God’s perfect wisdom, he has added the sacraments to the Word of the gospel for our benefit. He puts the promises of His gospel into tangible reality that we can see, feel, and taste. John Chrysostom stated: “Were we incorporeal (without a body), he would give us these things in a naked and incorporeal form. Now because our souls are implanted in bodies, he delivers spiritual things under things visible. Not that the qualities which are set before us in the sacraments are inherent in the nature of the things, but God gives them this signification.”
The Heidelberg Catechism puts the question/answer in this way:
Question 69. How art thou admonished and assured by holy baptism, that the one sacrifice of Christ upon the cross is of real advantage to thee?
Answer: Thus: That Christ appointed this external washing with water, (Matthew 28:19) adding thereto this promise, (Acts 2:38, Mark 16:16, Rom.6:3-4, among others) that I am as certainly washed by his blood and Spirit from all the pollution of my soul, that is, from all my sins, (1 Pet.3:21, Mark 1:4, Luke 3:3) as I am washed externally with water, by which the filthiness of the body is commonly washed away.
The assurance aspect of baptism works through the agency of the word, where God has taught us the great promises that are signified and sealed by it.
Unbelief rejects the God who ordained the sacraments. They should provide no assurance for those who do not put their faith in God alone, through Jesus. However, as we look back at our baptism, and partake of the Lord’s Supper, our faith should be confirmed and nourished as we contemplate the visible, tangible picture of His blessings that God has given to us.