The phrase “the keys of the kingdom” occurs only once in the bible, in Matthew 16:19, where Jesus is speaking to 
Peter: “I will give you the keys of the kingdom of heaven; and whatever you shall bind on earth shall have been bound in heaven and whatever you shall loose on earth shall have been loosed in heaven”. (NASB) What is the meaning of these “keys of the kingdom of heaven”?
Other places in the New Testament a key always implies authority to open a door and give entrance to a place or realm. Jesus says, “Woe to you lawyers! For you have taken away the key of knowledge; you did not enter yourselves, and you hindered those who were entering”. Luke 11:52
The “keys of the kingdom of heaven” therefore, at the very least, represent the authority to preach the gospel of Christ (cf. Matthew 16:16) and thus to open the door of the kingdom of heaven and allow people to enter.
Peter first used this authority by preaching the gospel at Pentecost (Acts 2:14-42). But the other apostles also were given this authority in a primary sense (they wrote the gospel in permanent form in the New Testament). And all believers have this “key” in a secondary sense, for they can all share the gospel with others, and thereby open the kingdom of heaven to those who will enter it.
But is there any other authority, in addition to this, that Jesus implies by the phrase “the keys of the kingdom of heaven”? As a matter a fact there is. There are two factors in this phrase that suggests the authority of the keys also includes “the authority to exercise discipline within the church”:
- The plural “keys” suggests authority over more than one door. Thus, more than simply entrance into the kingdom in implied; some authority within the kingdom is also suggested.
- Jesus completes the promise about the keys with a statement about “binding” and “loosing,” which closely parallels another saying of his in Matthew 18, in which “binding” and “loosing” mean placing under church discipline and releasing from church discipline:
“if he refuses to listen even to the church, let him be to you as a Gentile and a tax-gatherer. Truly I say to you, whatever you shall bind on earth shall have been bound in heaven; and whatever you loose on earth shall have been loosed in heaven”. (Matt. 18:17, 18 NASB)
The church can only declare and teach what God has already commanded in his Word. Nor can the authority of the keys involve authority to forgive sins in any absolute sense, because in scripture it is clear that that can only be done by God himself (Isaiah 43:25; 55:7; Mark 2:7, 10; Ps. 103:3; I John 1:9). Therefore the authority to carry out discipline in the church is an authority that must be carried out in accordance with the standards of scripture.
This teaching on the power of the keys has a significant application to individual Christians who begin to be subject to the discipline of a true church: Christians should submit to this discipline and not run from it, because God himself has also put them under discipline for that sin.
Jesus is teaching that church discipline will have heavenly sanction. But it is not as if the church must wait for God to endorse its actions after the actions have occurred. Rather, whenever the church enacts discipline it can be confident that God has already begun the process spiritually. Whenever it releases from discipline, forgives the sinner, and restores personal relationships, the church can be confident that God has already begun the restoration spiritually. (cf. John 20:23; Gal. 6:1; I Cor. 5; II Cor. 2:5-10.
Bibliography: Systematic Theology – An Introduction To Biblical Doctrine –
Wayne Grudem