Matthew 18:20

“For where two or three are gathered in my name, there am I among them.”  ESV

Two or three refers to witnesses, not worshipers. The context instructs you how to address a brother or sister who has sinned against you. Jesus drew from the Mosaic command for the assembly to only punish an accused person on the testimony of two or three witnesses (Deuteronomy 19:15). Jesus himself figuratively stands among the witnesses, authorizing the punishment (ostracism), if the offender has refused every attempt at restoration outlined here.

~ SR

Citation
Ruhmann, Scott. “Quick Notes: Matthew 18:20.” 27th Street Church of Christ. Access date: . http://www.churchofbend.com/qn/matt18-20.htm