Acceptable binding and loosing is founded in a hermeneutic that interprets scripture in light of scripture and, specifically, recognizes the priority of certain scriptural mandates.
Thus, even apart from the appeal to mercy, his loosing of the sabbath law is justified because "The Son of Man is Lord of the sabbath" (12:8).
Matt 18:15-20 presents the church's ministry of binding and loosing as necessary for the determination of who is to be subject to church discipline.
Specifically, 18:15-20 offers a perspective on how binding and loosing might function in a conflict situation, where there is disagreement.
Although this discussion of binding and loosing strikes some as new and potentially controversial, it has in some sense been the practice of the church throughout the centuries.