As much as we receive in faith

Calvin's Institutes (1559)
Book 4 of 4 - External Means by which God Invites Us into the Society of Christ and Holds Us Therein

Chapter 15 - Baptism

14-18 - Baptism and faith in the promise it signfies

14. We should receive baptism as from God. He gives it, and washes our soul as surely as water washes our body. "We should see spiritual things in physical [things]." It is not just a show, but "leads us to the present reality."

15. Cornelius is an example - he is baptized after receiving the Spirit and forgiveness, not to get more grace but as "a surer exercise of faith." Faith joins the reality to the sign. In baptism "we obtain only as much [grace] as we receive in faith." Baptism remains a sign of our confession - 1 Cor 12:13.

16. Baptism doesn't depend on the worth of the one administering it. A letter has the same value, whoever the carrier is. We are not baptized into the man, but into Christ. When sacraments are viewed superstitiously, this doesn't negate their effect for those who have faith.

17. Can one be unrepentant for a long time after their infant baptism, and even forever? Yes. Rom 3:3. And when they come to faith, God never had the Jews do a second circumcision (!) "However the covenant might be violated by them, the symbol of the covenant remained ever firm and inviolable by virtue of the Lord's institution."

18. Why were the believers in Acts 19 rebaptized by Paul, then? It was a baptism of the Spirit, by laying on of hands, not by water, like at Pentecost - Acts 1:5; 2:1-4. "If ignorance vitiates a previous baptism," the apostles would've needed rebaptizing after the resurrection or ascension.