Sons And The Father

Ut sitis filii Patris vestri... In quo enim alio cognoscetur quia filli summus Dei, nisi fuerimus similes Deo? Filii enim carnales frequenter similantur carnalibus patribus, in facie, aut in loquela, aut in risu, aut in aliquo corporis signo: filii autem spirituales in sanctitate. Et illi quidem etsi similes fuerint, laudem nullam merentur, et si dissimiles, nullam vituperationem, quia non est in potestate hominis qualem accipiat corporis qualitatem. Filii autem Dei, siquidem similes fuerint, laudandi sunt: si autem dissimiles, nimis vituperandi, quia in potestate unius ujusque est mensura faciendae justitiae. Si diligits eos, qui vos diligunt, quam mercedem habebitis? Qui amicos diligit, propter se diligit, non propter Deum, et ideo nullam habet mercedem: delectat enim eum ipsa dilectio. Qui autem inimicum suum diligit, non propter se diligit, sed propter Deum: ideo magnam habet mercedem, quia contradicit motibus suis. Ubi enim labour seminatur, illic metitiur fructus. Estote ergo perfecti, sicut et Pater vester perfectus est. Qui diligit amicum, peccatum quidem non facit, justitiam autem non operatur. Dimidium enim bonum est, hominem discedere a malo, et non sequi bonum: perfectum est autem, ut non solum fugiat malum, sed etiam faciat bonum. Ideo dicit, Perfecti estote, ut et amicos diligatis propter peccatum vitandum, et inimicos propter justitiam habendam: quoniam illud de poena liberat, hoc autem ducit in gloriam: nec enim est perfecta Dei imago, quae non per opera similat Deum. Opus Imperfectum in Matthaeum, Homilia XIII Source: Migne PG 56.703

That you may be sons of your Father... 1 For in what else shall it be known that we are sons of God unless we shall be like God? Carnal sons are often similar to carnal fathers, in face, in speech, in the way they smile, or in some other feature of the body, but spiritual sons are alike in holiness. And even if the former are similar, it merits no praise, and if they are dissimilar it earns no reproof, because it is not in the power of a man to take up some corporeal quality. But the sons of God, as much as they are similar so they are praiseworthy, and if they are dissimilar so they deserve to be blamed, because it is in the power of each one by the measure of righteous deeds. If you love those who love you, what reward shall you have? He who loves his friends, loves them for himself, and therefore he has no reward, for he delights in that affection. But he who loves his enemy, does not love for himself, but for God, and therefore he has a great reward, because he disputes his own inclinations. Where there is toil, there the fruit is reaped. Be perfect as your Father is perfect. He who loves a friend certainly does not commit a sin, but he does not work righteousness. It is only half a good to cut a man off from evil, and not to follow it with what is good. But he is perfect who not only flees sin, but even does good. Therefore He says, 'Be perfect'  so that you might love friends on account of the avoidance of sin, and love enemies for the possession of righteousness, since the former delivers from punishment and the latter leads to glory. There is no perfect image of God which is not made like God through deeds. Opus Imperfectum on Matthew, from Homily 13 1 Mt 5.48