On the authority of Jesus Christ. Jesus told the leaders of his Church, "Whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven" (Matthew 16:19, 18:18). The language of binding and loosing was a rabbinic way of referring to the ability to establish binding or rules of conduct for the faith community. It is thus especially appropriate that the references to binding and loosing occur in Matthew, the "Jewish Gospel."
Thus, the states: "BINDING AND LOOSING (Hebrew, . . . Rabbinical term for 'forbidding and permitting.' . . . "The power of binding and loosing as always claimed by the Pharisees. Under Queen Alexandra the Pharisees, says Josephus (1:5:2), 'became the administrators of all public affairs so as to be empowered to banish and readmit whom they pleased, as well as to loose and to bind.' . . . The various schools had the power 'to bind and to loose'; that is, to forbid and to permit (3b); and they could also bind any day by declaring it a fast-day (. . . 12a . . .). This power and authority, vested in the rabbinical body of each age of the Sanhedrin, received its ratification and final sanction from the celestial court of justice (9; 23b). "In this sense Jesus, when appointing his disciples to be his successors, used the familiar formula (Matt. 16:19, 18:18). 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. 23:2-4). In the same sense the second epistle of Clement to James II ('Clementine Homilies,' Introduction [A.D. 221]), 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.'" (3:215). Thus, Jesus invested the leaders of this Church with the power of making for the Christian community. This includes the setting of fast days (like Ash Wednesday). To approach the issue from another angle, every family has the authority to establish particular family devotions for its members. Thus, if the parents decide that the family will engage in a particular devotion at a particular time (say, Bible reading after supper), it is a sin for the children to disobey and skip the devotion for no good reason. In the same way, the Church as the family of God has the authority to establish its own family devotion, and it is a sin for the members of the Church to disobey and skip the devotions for no good reason (though of course if the person has a good reason, the Church dispenses him immediately).