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.
(Serm. in Mont. i. 23.) After that rule we must here understand of which John speaks, He gave them power to be made the sons of God. One is His Son by nature; we are made sons by the power which we have received; that is, so far as we fulfil those things that we are commanded. So He says not, Do these things because ye are sons; but, do these things that ye may become sons. In calling us to this then, He calls us to His likeness, for He saith, He maketh His sun to rise on the righteous and the unrighteous. By the sun we may understand not this visible, but that of which it is said, To you that fear the name of the Lord, the Sun of righteousness shall arise; (Mal. 4:2.) and by the rain, the water of the doctrine of truth; for Christ was seen, and was preached to good as well as bad.