Moreover, Chrysostom (Hom. x in the Opus Imperfectum, falsely ascribed to St. John Chrysostom) commenting on Mat. 5:19, "He that shall break one of these least commandments," says: "The commandments of Moses, Thou shalt not kill, Thou shalt not commit adultery, count for little in their reward, but they count for much if they be disobeyed. On the other hand the commandments of Christ such as, Thou shalt not be angry, Thou shalt not desire, are reckoned great in their reward, but little in the transgression." Now hatred is an internal movement like anger and desire. Therefore hatred of one's brother is a less grievous sin than murder. [Summa Theologica Second Part, Treatise on Theological Virtue Question 34.4]
and again:
Otherwise; the precepts of Moses are easy to obey; “Thou shalt not kill. Thou shalt not commit adultery.” The very greatness of the crime is a check upon the desire of committing it; therefore the reward of observance is small, the sin of transgression great. But Christ’s precepts, “Thou shalt not be angry, Thou shalt not lust,” are hard to obey, and therefore in their reward they are great, in their transgression, ‘least.’ It is thus He speaks of these precepts of Christ, such as “Thou shalt not be angry, Thou shalt not lust,’ as ‘the least;’ and they who commit these lesser sins, are the least in the kingdom of God; that is, he who has been angry and not sinned grievously is secure from the punishment of eternal damnation; yet he does not attain that glory which they attain who fulfil even these least.(same source, Cantena Aurea chapter 5)
and again:
As that, Thou shalt not lust, was not spoken to the flesh, but to the spirit, so in this the flesh indeed is not able to love its enemy, but the spirit is able; for the love and hate of the flesh is in the sense, but of the spirit is in the understanding. If then we feel hate to one who206 has wronged us, and yet will not to act upon that feeling, know that our flesh hates our enemy, but our soul loves him.(ibid)
The original author (or his source) clearly used a Diatessaron.
