Matthew 18:20 - Ellicott's Commentary On The Whole Bible

Where two or three... — The true meaning of the words is well embodied in the well-known patristic axiom, Ubi tres, ibi Ecclesia (“Where three are there is a church”). The strength of the Christian society was not to be measured by a numerical standard, but by its fulfilment of the true conditions of its life. The presence of Christ was as true and mighty, His communion with His Church as real, when His followers were but as a remnant, as when they were gathered in the great congregation. He would be with the “two or three” (there is, perhaps, a special reference to the self-same words in Matthew 18:16), to plead for them as the great High Priest, to impart Himself to them, to ratify their decisions.