By guidance from the Spirit. YLT renders the text in 16:19 ".... whatever thou mayest bind upon the earth shall be having been bound in the heavens, and whatever thou mayest loose upon the earth shall be having been loosed in the heavens.'" the NIV footnotes that "... will be
d bound in heaven..." could be read instead as Or '
will have been', suggesting that through Peter more would be conveyed over time. This isn't a power of Peter, but rather it's more that Peter was a vehicle. Later, when Peter errs to refuse to eat with the uncircumcised for a time, Paul confronts and corrects him. The Spirit can work through more than only Peter of course. In chapter 18 this seems to be told to them all to be conferred to all of them. Again in John 20, verses 21 through 23, the Spirit comes onto them all, and all of them can then act from the Spirit, as the Spirit is deciding, in the future. Not one of them only, but all. Initially, they are the evangelists at this moment in the gospels, receiving the commission, the first of many. The Spirit will be on them, and they will perform great signs/miracles. The Spirit will guide them in what to say when they are put on trial.