The Church
Matthew 18:17
And if he will not hear them: tell the church. And if he will not hear the church, let him be to thee as the heathen and publican.
Context of the passage
Jesus outlines a process of fraternal correction for a sinning brother, escalating from private confrontation to witnesses to the whole visible community, the 'church.'
Catholic reading
Jesus presupposes a single, visible, identifiable community with real authority to make binding judgments in disputes, a structured, hierarchical Church rather than an invisible collection of believers united only by private faith.
Common objection
'The church' here just means the local gathered congregation exercising simple communal discipline, not a universal hierarchical institution with binding doctrinal authority.
Response
Even granting a local congregation is in view, Jesus assumes this community possesses genuine authority whose verdict determines one's standing ('let him be to thee as the heathen'), and this local authority is the same 'binding and loosing' power given to the apostles collectively in the same chapter (v.18), rooted in the universal authority given to Peter and the apostles.