Heidelberg Catechism Lord's Day 31

THE POWER OF THE KEYS  By the power of the keys the kingdom of heaven is  opened to believers and shut against unbelievers by  the appointed officers of the church, according to the  command of Christ, by the preaching of the Gospel  and Christian discipline. (Q. 83–85.) Question 83  Q. What is the Office of the Keys?  A. The preaching of the Holy Gospel and Christian discipline; by these two the kingdom of heaven is opened to believers and shut against unbelievers. Question 84  Q. How is the kingdom of heaven opened and shut by the preaching of the Holy Gospel?  A. In this way: that, according to the command of Christ, it is proclaimed and openly witnessed to believers, one and all, that as often as they accept with true faith the promise of the Gospel, all their sins are really forgiven them of God for the sake of Christ’s merits; and on the contrary, to all unbelievers and hypocrites, that the wrath of God and eternal condemnation abide on them so long as they are not converted. According to this testimony of the Gospel, God will judge men both in this life and in that which is to come. Question 85  Q. How is the kingdom of heaven shut and opened by Christian discipline?  A. In this way: that, according to the command of Christ, if any under the Christian name show themselves unsound either in doctrine or in life, and after several brotherly admonitions do not turn from their errors or evil ways, they are complained of to the Church or to its proper officers; and, if they neglect to hear them also, are by them denied the holy sacraments and thereby excluded from the Christian communion, and by God Himself from the kingdom of Christ; and if they promise and show real amendment, they are again received as members of Christ and His Church.