Text 31. Vers. 43. Yee have heard, that it hath beene said, Thou shalt love thy neighbor, and hate thine enemy.John Mayer, A Commentary Upon the New Testament, Vol. 1 (London: Printed by Thomas Cotes, for John Bellamie, and are to be sold at his shoppe in Cornehill, at the sign of the three Golden Lyons, neere the Royall Exchange, 1631), 111. Mayer cites Augustine's De sermone Domini in monte c. 41, c. 42, Enchiridon c.73, and Contra Faustum Manichaeum lib. 19. c. 14 [see c. 24 or NPNF, 1st Series, 4:248] in the margin. Some of these references seem to be incorrect.
August. These last words are not to be taken, as the words of one commanding a just man, but tollerating a weake one. And herein the law is not against the Gospel, for Paul saith, that some men are hatefull unto God, and therefore may be hated of us; but they are to be hated onely in respect of their vices, and not of their persons, which be Gods creatures; this being not understood, made the Scribes to thinke, that they might hate the very person of their enemies. But Christ teacheth to love our enemies, setting downe precepts for the perfect, unto which every faithfull person ought to strive by prayer, and indeavour to attaine.
Mayer then comments:
And with Augustine, I think, that there is an hatred of enemies agreeable to Gods word, viz. the hatred of their vices, but not of their persons, which are notwithstanding to be loved, and prayed for.Ibid., 112.
Bio on Mayer:
DNB
Note: The modern slogan that we should "love the sinner but hate the sin" is one that, at least conceptually, goes back to Augustine, but is not understood by many today. For him and others (i.e. Aquinas, Calvin, Rutherford, Jenkyn, Manton, Polhill, Mayer, etc.), this idea was the same as saying that Christians should love lost people as creatures of God and yet hate them as sinners. They may be loved and hated at the same time but in different respects, even as God both loves and hates the unbelieving elect at the same time but in different respects (see Charnock and Pawson).