Cyprian of Carthage, On the Unity of the Church 13
When He gave the law of prayer, He added these words: 'And when you stand praying, forgive whatever you have against anyone, so that your Father in heaven may also forgive you your sins' (Mark 11:25). He calls back from the altar anyone who comes to the sacrifice with a quarrel, and He commands that person first to be reconciled with his brother; then, returning in peace, to offer his gift to God (Matthew 5:23-24). For God did not look with favor on Cain's gifts (Genesis 4:3-5); the one who did not have peace with his brother because of jealous discord could not have God as his peacemaker. What peace, then, do the enemies of brothers promise themselves? What sacrifices do they imagine they are offering as rival priests? Or do they suppose that Christ is with them when they gather, when they are gathering outside Christ's Church?
Latin
Ideo et cum orandi legem daret, addidit dicens: Et cum steteritis ad orationem, remittite si quid habetis adversus aliquem, ut et Pater vester qui in coelis est remittat vobis peccata. Et ad sacrificium cum dissensione venientem revocat ab altari, et jubet prius concordare cum fratre, tunc cum pace redeuntem Deo munus offerre, quia nec ad Cain munera respexit Deus: neque enim pacatum habere Deum poterat, qui cum fratre pacem per zeli discordiam non habebat. Quam sibi igitur pacem promittunt inimici fratrum, quae sacrificia celebrare se credunt aemuli sacerdotum? An secum esse Christum cum collecti fuerint opinantur, qui extra Christi Ecclesiam colliguntur?