The following is an excerpt from
The MacArthur New Testament Commentary on Matthew 16.
“I will give you the keys of the kingdom of heaven; and whatever you shall bind on earth shall be bound in heaven, and whatever you shall loose on earth shall be loosed in heaven.” (Matthew 16:19)
Jesus spoke about the authority of the church. “I will give you the keys of the kingdom of heaven,” He said; “and whatever you shall bind on earth shall be bound in heaven, and whatever you shall loose on earth shall be loosed in heaven.”
The Lord was addressing Peter as representative of the Twelve, telling him that whatever you shall bind, that is, forbid, on earth shall be bound in heaven and that whatever you shall loose, that is, permit, on earth shall be loosed in heaven. He told Peter and the Twelve, and by extension all other believers, that they had the astounding authority to declare what is divinely forbidden or permitted on earth!
Shortly after His resurrection Jesus told the disciples, “If you forgive the sins of any, their sins have been forgiven them; if you retain the sins of any, they have been retained” (John 20:23). In giving instruction for church discipline to all His people, Jesus said that, if a sinning believer refuses to turn from his sin after being counseled privately and even after being rebuked by the entire congregation, the church not only is permitted but obligated to treat the unrepentant member “as a Gentile and a tax-gatherer” (Matt. 18:15–17). He then said to the church as a whole what He earlier had said to Peter and to the other apostles: “Truly I say to you, whatever you shall bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven” (v. 18). In other words, a duly constituted body of believers has the right to tell an unrepentant brother that he is out of line with God’s Word and has no right to fellowship with God’s people.
Christians have such authority because they have the truth of God’s authoritative Word by which to judge. The source of the church’s authority is not in itself, anymore than the source of the apostles’ authority was in themselves or even in their office, exalted as it was. Christians can authoritatively declare what is acceptable to God or forbidden by Him because they have His Word. Christians do not determine what is right or wrong, forgiven or unforgiven. Rather, on the basis of God’s own Word, they recognize and proclaim what God has already determined to be right or wrong, forgiven or unforgiven. When they judge on the basis of God’s Word, they can be certain their judgment corresponds with the judgment of heaven.
If a person declares himself to be an atheist, or to be anything other than a believer in and lover of the Lord Jesus Christ, Christians can say to that person with absolute certainty, “You are under God’s judgment and condemned to hell,” because that is what Scripture teaches. If, on the other hand, a person testifies that he has trusted Christ as his saving Lord, Christians can say to him with equal certainty, “If what you say is true, then your sins are forgiven, you are a child of God, and your eternal destiny is heaven” The authority of the church lies in the fact that it has heaven’s word on everything “pertaining to life and godliness, through the true knowledge of Him who called us by His own glory and excellence” (2 Pet. 1:3). When believers are in agreement with God’s Word, God is in agreement with them. Believers can declare a person’s spiritual state with divinely granted authority by comparing that person to the Word of God.