Heidelberg Catechism – Lord’s Day 31
Q. What is the office of the keys?
A. The preaching of the holy and Christian discipline. By these two means the kingdom of heaven is opened to believers and shut against unbelievers.
Q. How is the kingdom of heaven opened and shut by the preaching of the holy gospel?
A. In this way: The kingdom of heaven is opened when it is proclaimed and openly testified to believers, one and all, according to the command of Christ, that as often as they accept the promise of the gospel with true faith all their sins are truly forgiven them by God for the sake of Christ’s gracious work. On the contrary, the wrath of God and eternal condemnation fall upon all unbelievers and hypocrites as long as they do not repent. It is according to this witness of the gospel that God will judge the one and the other in this life and in the life to come.
Q. How is the kingdom of heaven shut and opened by Christian discipline?
A. In this way: Christ commanded that those who bear the Christian name in an unchristian way either in doctrine or in life should be given brotherly admonition. If they do not give up their errors or evil ways, notification is given to the church or to those ordained for this by the church. Then, if they do not change after this warning, they are forbidden to partake of the holy Sacraments and are thus excluded from the communion of the church and by God himself from the kingdom of Christ. However, if they promise and show real amendment, they are received again as members of Christ and of the church.