Origen
Catena Aurea · Matthäusevangelium 18
Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven. Again I say unto you, That if two of you shall agree on earth as touching any thing that they shall ask, it shall be done for them of my Father which is in heaven. For where two or three are gathered together in my name, there am I in the midst of them.
And this also is the reason why our prayers are not granted, because we do not agree together in all things upon earth, neither in doctrine, nor in conversation. For as in music, unless the voices are in time there is no pleasure to the hearer, so in the Church, unless they are united God is not. pleased therein, nor does He hear their words.