Rabbinical term for "forbidding and permitting." The expression "asar" (to bind herself by a bond) is used in the Bible (Num. xxx. 3 et seq.) for a vow which prevents one from using a thing. ... The various schools [of Jewish theology -- EBB] had the power "to bind and to loose"; that is, to forbid and to permit (Ḥag. 3b); and they could bind any day by declaring it a fast-day (Meg. Ta'an. xxii.; Ta'an. 12a; Yer. Ned. i. 36c, d). This power and authority, vested in the rabbinical body of each age or in the Sanhedrin..., received its ratification and final sanction from the celestial court of justice (Sifra, Emor, ix.; Mak. 23b).
In this sense Jesus, when appointing his disciples to be his successors, used the familiar formula (Matt. xvi. 19, xviii. 18). By these words he virtually invested them with the same authority as that which he found belonging to the scribes and Pharisees who "bind heavy burdens and lay them on men's shoulders, but will not move them with one of their fingers"; that is, "loose them," as they have the power to do (Matt. xxiii. 2-4). In the same sense, in the second epistle of Clement to James II. ("Clementine Homilies," Introduction), Peter is represented as having appointed Clement as his successor, saying: "I communicate to him the power of binding and loosing so that, with respect to everything which he shall ordain in the earth, it shall be decreed in the heavens; for he shall bind what ought to be bound and loose what ought to be loosed as knowing the rule of the church."
Quite different from [and yet not opposed to? -- EBB] this Judaic and ancient view of the apostolic power of binding and loosing is the one expressed in John xx. 23, where Jesus is represented as having said to his disciples after they had received the Holy Spirit: "Whosesoever sins ye remit, they are remitted unto them; and whosesoever sins ye retain, they are retained." It is this view which, adopted by Tertullian and all the church fathers, invested the head of the Christian Church with the power to forgive sins, the "clavis ordinis," "the key-power of the Church."
In this light, consider Matthew 23:1-3,
1 Then Jesus spoke to the multitudes and to His disciples, 2 saying: "The scribes and the Pharisees sit in Moses' seat. 3 Therefore whatever they tell you to observe, that observe and do, but do not do according to their works; for they say, and do not do.
and Matthew 16:13ff.,
13 When Jesus came into the region of Caesarea Philippi, He asked His disciples, saying, "Who do men say that I, the Son of Man, am?" ...
16 Simon Peter answered and said, "You are the Christ, the Son of the living God."
17 Jesus answered and said to him, "Blessed are you, Simon Bar-Jonah, for flesh and blood has not revealed this to you, but My Father who is in heaven. 18 And I also say to you that you are Peter, and on this rock I will build My church, and the gates of Hades shall not prevail against it. 19 And I will give you the keys of the kingdom of heaven, and whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed[d] in heaven."
And, finally, consider the words of St. Macarius of Egypt (371 A.D.):
"Moses was succeeded by Peter, who had committed to his hands the new Church of Christ, and the true priesthood." (Macarius, Hom. xxvi. n. 23, p. 101)
Very modestly, it is parallels and admissions like these that deepen my appreciation for the Catholic Church: it's got all the divine structures and rhythyms (and blotches) of Judaism but with the astounding bonus of forgiveness in Christ and the life of the Holy Spirit! Christ came not to abolish the Law but to fulfill, deepen and redeem it (cf. Mth 5:17). That promise is much of the basis for my Catholic faith.
(P.S. Such thoughts are running through my head partly because I recently made a contribution to a dialogue I've been having with a [no offense, D.] self-styled Jewish Christian. Writing that letter helped me see more clearly the continuity between Judaism and the Church (as I hope it helps my dialogue partner see). On top of that, I'm reading Roy Schoeman's enjoyable book, Salvation Is From the Jews. Mazel tov!)