Augustine of Hippo
Catena Aurea · Matthäusevangelium 5
Ye have heard that it hath been said, Thou shalt love thy neighbour, and hate thine enemy. But I say unto you, Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you and persecute you; That ye may be the children of your Father which is in heaven: for He maketh His sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust. For if ye love them which love you, what reward have ye? do not even the Publicans the same? And if ye salute your brethren only, what do ye more than others? do not even the Publicans so? Be ye therefore perfect, even as your Father which is in heaven is perfect.
(Enchir. 73.) These indeed are examples of the perfect sons of God; yet to this should every believer aim, and seek by prayer to God, and struggles with himself to raise his human spirit to this temper. Yet this so great blessing is not given to all those multitudes which we believe are heard when they pray, Forgive us our debts, as we forgive our debtors.