12 Nor let any deceive themselves by a futile interpretation, in respect of the Lord having said, “Wheresoever two or three are gathered together in my name, there am I in the midst of them.” Corrupters and false interpreters of the Gospel quote the last words, and lay aside the former ones, remembering part, and craftily suppressing part: as they themselves are separated from the Church, so they cut off the substance of one section. For the Lord, when He would urge unanimity and peace upon His disciples, said, “I say unto you, That if two of you shall agree on earth touching anything that you shall ask, it shall be given you by my Father which is in heaven.
For wheresoever two or three are gathered together in my name, I am with them;” showing that most is given, not to the multitude, but to the unanimity of those that pray. “If,” He says, “two of you shall agree on earth:”He placed agreement first; He has made the concord of peace a prerequisite; He taught that we should agree firmly and faithfully. But how can he agree with any one who does not agree with the booty of the Church itself, and with the universal brotherhood? How can two or three be assembled together in Christ's name, who, it is evident, are separated from Christ and from His Gospel?
For we have not withdrawn from them, but they from us; and since heresies and schisms have risen subsequently, from their establishment for themselves of diverse places of worship, they have forsaken the Head and Source of the truth. But the Lord speaks concerning His Church, and to those also who are in the Church He speaks, that if they are in agreement, if according to what He commanded and admonished, although only two or three gathered together with unanimity should pray— though they be only two or three— they may obtain from the majesty of God what they ask.
“Wheresoever two or three are gathered together in my name, I,” slays He, “am with them;”that is, with the simple and peaceable— with those who fear God and keep God's commandments. With these, although only two or three, He said that He was, in the same manner as He was with the three youths in the fiery furnace; and because they abode towards God in simplicity, and in unanimity among themselves, He animated them, in the midst of the surrounding flames, with the breath of dew: in the way in which, with the two apostles shut up in prison, because they were simple-minded and of one mind, He Himself was present; He Himself, having loosed the bolts of the dungeon, placed them again in the market-place, that they might declare to the multitude the word which they faithfully preached.
When, therefore, in His commandments He lays it down, and says, “Where two or three are gathered together in my name, I am with them,” He does not divide men from the Church, seeing that He Himself ordained and made the Church; but rebuking the faithless for their discord, and commending peace by His word to the faithful, He shows that He is rather with two or three who pray with one mind, than with a great many who differ, and that more can be obtained by the discordant prayer of a few, than by the discordant supplication of many.
Source: The Treatises of Cyprian (New Advent)