Christ tells Peter:
Whatever you bind on earth will have been bound in heaven, and whatever you loose on earth will have been loosed in heaven (Matt 16:19).
The talk of “binding and loosing” is commonly connected to the Pharisees and their presumed authority as rabbis. Assuming one opts for this “future perfect passive” interpretation of the relevant Greek phrases, it seems to me that there are two possible ways of interpreting what Christ says here to Peter.
According to the prospective reading, Christ is telling Peter that his future exercise of his authority to bind and loose will be guided by the providence of God. What God will have already decided in eternity, Peter will also decide in time, arriving at the right conclusions by God’s help. Moreover, Peter is conferred (either as a whole or in part) the authority the Pharisees took themselves to have. This presumably also entails that such a promise be passed down to the successor to the seat of Peter, as well.
According to the retrospective reading, Christ is telling Peter that he himself will only bind or loose what God will already have (clearly) bound or loosed. This is in contradistinction to the Pharisees, who bind even where God has not bound and loosen where it does not make sense. An example: The Pharisees invent rules and bind and loosen contrary to God’s Law (Matt 15; 23). Peter, on the other hand, permits the Gentiles to be baptized after he already sees that they have received the Holy Spirit and thus have been received by God (Acts 10). God made a decision first, and Peter went along with it.
On the prospective reading, Peter has a charism of infallibility. He is endowed with a unique authority as the single possessor of an office. He is assured that his exercise of his authority will be guided by God “behind the scenes.” He can take “steps forward” into the future, changing things or developing them beyond their starting points, in the conviction that God has empowered him to do so and will protect him from error. The divine protection is concurrent with Peter’s own exercise of his judgment and reasoning, so that he becomes an instrument in God’s hands.
On the retrospective reading, Peter is not promised a charism of infallibility, nor is he endowed with any special, autonomous authority. There are two ways of interpreting the use of the indicative mood in Christ’s statement.
One way: It is an assurance and prediction of the future. In effect, Christ tells and assures Peter, to whom He has just handed to keys to the kingdom of heaven, that he will not in fact bind or loose incorrectly. This does not mean that Peter will possess any special gift of infallibility, but only that, as things will actually turn out, he will not misuse his authority. How can he not misuse his authority if he is not infallible? Easy. God could ensure this by acting clearly and unambiguously to guide Peter’s decisions, as in Acts 10. There is no need to be infallible where things are clear.
Another way: It is an encouragement and a calling. In this way, it would be like what happens when someone facing a challenge firmly tells himself: “I can do this.” Or like when one strongly encourages a troubled friend: “You will get past this and you will succeed.” Christ attempts to make Peter into a proper leader for the Church precisely by telling him that he will be one. It is an indicative statement with an implicit imperatival character.
I am personally more strongly inclined toward the first interpretation. But in either case, the essence of the retrospective reading is the implicit contrast between Peter and the Pharisees. Throughout the Gospel of Matthew, it is clear that Christ believes that the Pharisees do not bind and loose correctly because they do not understand and stick to the word of God. Peter, however, will not turn out like that. That is the essence of what Christ tells him in Matt 16:19, according to the retrospective reading.
On the prospective reading, God makes “public” or “visible” His eternal decision to bind or loose through Peter. Peter becomes the mouthpiece and hand of God. On the retrospective reading, God makes His decision to bind or loose “publicly” apart from Peter, and Peter is expected to follow God’s lead. Peter may be a leader of the Church, but God is outside of Peter just as He is outside of any other person in the Church.
Another way of appreciating the difference in nuance between the two readings is by attention to emphasis.
According to the prospective reading, the emphasis would lie as follows: Whatever you bind on earth will have been bound in heaven, etc. Placing the emphasis in this way accentuates the open horizon of the future: there is no telling now what Peter will have to bind or loose in the future, only that God will have been guiding him the whole time all the same. He is concerned only to endow a certain authority on Peter as the “rock” on which the Church is built. That is why it is called the pro-spective reading: because it has Peter looking forward to an indefinite, open future and to all the problems in it which he has been authorized to address.
According to the retrospective reading, the emphasis would lie as follows: Whatever you bind on earth will have been bound in heaven, etc. Placing the emphasis in this way distinguishes Peter and his exercise of this authority from the Pharisees. The central concern is not to endow Peter with some especially unique authority. Nor does what Christ say here to Peter necessarily apply to any person who claims (rightly or not) to have inherited Peter’s office. From the fact that Peter is told that he will follow God’s lead, it doesn’t follow that everyone or even anyone after him will do so. Rather, it is to emphasize the distinct way in which Peter as a particular individual will exercise his authority in comparison to the Pharisees. Whereas the Pharisees had bound and loosed inappropriately, Peter will do so appropriately insofar as he himself will be following the lead of God, only binding where God will have bound and only loosing where God will have loosed, as for example in Acts 10. That is why it is called the retro-spective reading: because it has Peter looking back to what God has already bound or loosed before making a decision on his own.
Matt 16:19 has been used to argue for the unique authority of the Bishop of Rome. But the retrospective reading does not generate a doctrine of the papacy. This is because it does not conceive of Peter as having been endowed with a charism of infallibility that belongs to his position of authority as such and thus could be inherited by someone else. Christ is not promising Peter infallibility, nor is He is speaking about anyone except Peter as an individual. Christ is only making an indicative statement about the way Peter’s own exercise of his authority to bind and loose will turn out in time, namely that it will correspond retrospectively to what God will have bound and loosed, i.e. that Peter will be following God’s lead, and this in contradistinction to the Pharisees who went off on their own a long time ago. Nothing about this entails that a future successor to the seat of Peter, assuming that there is such a thing, could not make mistakes, binding what heaven will not have bound, loosing what heaven will not have loosed.
In summary: The prospective reading understands Christ to have established Peter (and his successors, by implication) as the mouthpiece of God, by means of which God’s eternal decisions to bind or loosed will be communicated with the Church. It sees Peter being endowed with an authority which orients him toward an indefinite and open future. The retrospective reading understands Christ to have assured Peter that he in particular, unlike the Pharisees, will be guided by God in his decisions to bind and loose. Neither Peter nor his successors (if there be any) are set up as the mouthpieces of God. Rather, Peter is assured that he in particular will lead the Church by teaching it to look back at what God has, in their time, clearly bound or loosed apart from Peter’s own public position on the issue. Peter is not the mouthpiece of God in any special sense, nor is he infallible. He is only charged with leading the Church to recognize what God has clearly done and is clearly doing.
Thus, I think that if one opts for the retrospective reading of Christ’s words to Peter in Matt 16:19, then the text would not support a doctrine of the papacy. This is because the text would not involve Christ conferring infallibility on Peter. I think the retrospective reading is compatible both with “Orthodox” or “Anglican” understandings of the episcopate, as well as with non-episcopal conceptions of church government. But that discussion is not as important to me for now.