Matthew 16:19

The keys of the kingdom of heaven] i.e. the keys of the earthly Church, not of heaven itself. Peter is not here compared to the porter of a house, who has only the key of the gate, but, since he possesses all the keys, to a house-steward exercising full authority over the house and all its inmates, in the master's name: cp. Isaiah 22:15. The power of the keys is, (1) the power to govern the Church; (2) the power to exercise discipline in it; (3) the power to decide who shall be admitted into it, and on what conditions (subject, of course, to the Law of Christ); (4) and indirectly, since the steward provides food for all the household, the ministry of the Word and Sacraments. Government and discipline, however, and not ministry, are the main ideas. The narrower interpretations of the power of the keys, as that it is the power to admit into the Church by the preaching of the gospel, are not so much erroneous as insufficient. The figure in Luke 11:52; ('the key of knowledge') is different. The best NT. parallel is Revelation 3:7.

Bind.. loose] These words, unintelligible in Greek and English, become full of meaning when traced back to the original Aramaic.

Every rabbi or scribe received at his ordination, which was, like that of the Christian Church, by the laying on of hands, the power to bind and to loose, i.e. to decide with authority what was lawful and unlawful to be done, or orthodox and unorthodox to be believed. To bind was to declare unlawful, to loose was to declare lawful. We read, for example, that 'Rabbi Meir loosed (i.e. permitted) the mixing of wine and oil, and the anointing of a sick man on the sabbath'; that Babbi Jochanan said, 'They necessarily loose (i.e. permit) saluting on the sabbath,' and 'Concerning gathering wood on a feast day, the school of Shammai binds (i.e. forbids) it,—the school of Hillel looses (i.e. permits) it.' The power, therefore, which Christ here promised to Peter and the other apostles was the power to decide with authority questions of faith and morals in the Christian Church,—the power to fix the moral standard and to determine the Christian creed. In the exercise of this authority the apostles 'loosed' the prohibitions of the Mosaic Law first to the Gentiles (Acts 15), and finally to the Jews (Mark 7:9 RV, see on Matthew 15:1), decided what standard of morality should be enforced in the society, and pronounced with authority in controversies of faith.

When the Jewish rabbis differed upon an important matter of doctrine or practice, a conference was held, and the judgment of the majority was held to be authoritative. Similarly the apostolic power of 'binding and loosing' was intended to be exercised collectively, and great deference was paid both in the apostolic and in subsequent ages to the decisions of synods (Acts 15).

In heaven] It is promised that God Himself will ratify the 'binding and loosing' of the earthly Church, when these powers are duly and legitimately exercised. 'Binding and loosing' is different from the power of remitting and retaining sins, for which see John 20:23.