Origen — as excerpted in the Catena Aurea on Matthew 18:18-20

“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.”