Hi friend and collegue, Rev. Wes White, has a wonderful explanation of the efficacy of the sacraments, that is, what they accomplish, on his blog here.

In my recent series of eleven sermons on the sacraments, I spoke of this same theme:

How Does Baptism Assure Us?
The Fourth Sermon on the Sacraments

CONGREGATION OF JESUS CHRIST:

WE HAVE seen that God has attached his grace to outward and ordinary means, the preaching of the Gospel, baptism, and the Lord’s Supper (Q&A 65). Baptism and the Lord’s Supper are what we call “sacraments” because they are outward and visible signs and seals of God’s inward and invisible grace in Christ (Q&A 66). As means of grace, the Word and sacraments are intended to point our faith to Jesus Christ alone, and not to themselves or to ourselves (Q&A 67). Finally, there are only two sacraments, baptism and the Lord’s Supper (Q&A 68).

This evening we want to begin dealing with baptism by looking at Heidelberg Catechism, Q&A 69, “How is it signified and sealed to you in Holy Baptism that you have part in the one sacrifice of Christ on the cross? Thus: that Christ instituted this outward washing with water and joined to it this promise, that I am washed with His blood and Spirit from the pollution of my soul, that is, from all my sins, as certainly as I am washed outwardly with water, whereby commonly the filthiness of the body is taken away."

The question we are faced with is not whether baptism assures us, but how baptism assures us?

It Presupposes Communion
In the first place, the assurance of baptism presupposes faith. Did you catch the language of our Catechism, when it asks, “How is it signified and sealed to you . . . that you have part in the one sacrifice of Christ?” This is a question asked of believers in Jesus. Notice again that language of having a part in Christ’s sacrifice. That comes from Q&A 65, which asks, “Since, then, we are made partakers of Christ and all his benefits by faith only, where does this faith come from? The Holy Spirit works faith in our hearts by the preaching of the Holy Gospel and confirms it by the use of the holy sacraments.”

This is so important in our day and age when there are those in the Reformed community saying what Rome and Lutherans say: all baptized people are regenerated, united to Christ, and saved. But when Q&A 69 gives it’s answer, it is the one who has already believed that answers: "that I am washed with His blood and Spirit from the pollution of my soul, that is, from all my sins, as certainly as I am washed outwardly.”

Our Catechism speaks this way because Scripture speaks this way. When God gave Abraham the sign of the covenant of circumcision in Genesis 17, he had already “believed the Lord” who “counted it to him as righteousness” (15:6). This is why Paul speaks in Romans 4 that circumcision was given to Abraham after he believed as a seal, that is, an assurance, that he was righteous before God by faith.

You see, what has happened so often in the history of God’s people, whether with Israel or with the Roman Church or with modern innovators, is that we place our trust in the sign itself. This is why Jeremiah spoke of the Lord’s punishment of all who were “circumcised merely in the flesh” (9:25). He goes on to say this means all the nations, but even the Israelites, because they were “uncircumcised in heart” (9:26). Israel had the sign, but they did not embrace what it signified in Jesus Christ.

Do not trust in the water, beloved, but him who ordained the water. Indeed, as John Calvin said in speaking of baptism, “We obtain only as much as we receive in faith” (Institutes, 4.15.15).

So why do we baptize children, if the assurance of baptism presupposes communion with Christ through faith? We will come to that when we deal with Q&A 74.

It Promises Comfort
Baptism assures us because it promises comfort to those who embrace the Savior. The language of the Catechism is so amazing here: “How is it signified and sealed to you [the wretched sinner] in Holy Baptism that you [the Christian who constantly stumbles and falls] have part in the one sacrifice of Christ?” It promises comfort to those in need of such comfort. It promises comfort to the comfortless.

As circumcision was the seal of the righteousness that Abraham had by faith, baptism specifically comforts the Christian: “I am washed with His blood and Spirit from the pollution of my soul, that is, from all my sins, as certainly as I am washed outwardly with water.” The language of certainty brings us comfort, for as certainly, as truly, as really as outward water has touched our bodies so certainly, truly, and really has the blood and Spirit of Christ touched our souls. And the Catechism gives us an analogy: just as water is used to wash our bodies, so the blood and Spirit of Christ is used to wash our souls. But the blood and Spirit of Christ are not cleansing agents that we need to reapply because they didn’t do the job!

Think of what Paul’s words meant to the Corinthians. He speaks a word of condemnation and exclusion from God’s kingdom to “the unrighteous,” to those whose lives are characterized by sexually immorality, idolatry, adultery, homosexuality, nor thievery, greed, drunkenness, reviling, and swindling. Who can escape such a list? Who can see he or she has kept free of such sins, which are only a partial list, given as examples? But Paul says, “And such were some of you” (1 Cor. 6:10). “But,” he goes on to say—and you’ve got to appreciate the order in which he says what he says—“you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.” Why does he begin with the language of washing? Because sanctification and justification (which, we will see are the benefits of baptism in Q&A 70 next Lord’s Day) are works that God does inwardly in us. Baptism, this “washing” of which Paul speaks, is what we can see, feel, remember, and experience!

It Produces Confidence
Baptism assures us because it produces confidence. You were excluded from God’s kingdom, but God has included you! You can say, “I am washed with His blood and Spirit. I have part in the one sacrifice of Christ.”

In the name of the Father, and of the Son, and of the Holy Spirit. Amen.