Thanks for your recent article.
A number of distinctions need to be made.
1. Different Christian traditions have different views of the Old Testament. In general, those in the Lutheran, Baptist, Anabaptist, and fundamentalist tradition see more discontinuity between Old Testament ethics and New Testament ethics than those in the Reformed (=Calvinist) tradition. A Calvinist like myself sees the moral law of God as the same, whether under the Mosaic Covenant or the New Covenant. This view is fairly common among conservative Presbyterians.
2. I would add that some Christian traditions change over time. Roman Catholicism, for most of its history, has been very exclusive and militant. But in the 20C it became quite inclusive and pacifistic. There's a world of difference between John-Paul II and Julius II or Innocent XIII.
3. The scope of God's love also differs with different traditions. Most Christian traditions believe that God loves everyone--equally and without exception.
However, the Augustinian tradition, which is taken up in the Reformed (Calvinist) tradition, sees the love of God as intensive rather than extensive. Just as the Jews were a chosen people as over against the multitude of the heathen in Old Testament times, God does not show his favor to everyone alike. Rather, the love of God is like marital love--exclusive and intensive rather than inclusive and extensive. The difference is between a love which is broad, but shallow, and a love which is narrow, but deep.
4. By the same token, a Calvinist would say that God loves a sinner, not because the sinner is lovable or at all deserving of love. To the contrary, God loves a sinner out of his sheer mercy and grace.
5. At the same time, there is also a doctrine of divine judgment in both the Old Testament and the New Testament. There is such a thing as damnation and hell. This is true of almost every Christian tradition, although some have liberalized.
6. God's attitude towards the sinner is, of course, germane to our attitude towards the sinner. There is a sort of folkloric version of Christian ethics that is popular in many churches. It is based on a very lopsided and hermeneutically naïve reading of the Gospels. It contains a grain of truth, but a half-truth.
7. One element is the fallacy of unconditional forgiveness. Many Christians believe it to be their Christian duty to forgive everyone, period.
One thing they forget is that the Gospels were written to the church, to the Christian community, just as the Mosaic Law was addressed, in the first place, to the covenant community.
This doesn't mean that there's one standard for insiders, and a totally different standard for outsiders. But what makes a faith-community a community is a certain level of mutuality and reciprocity. One cannot transfer this without qualification to those who are not signatories to a common ethic.
Even in the church, forgiveness is contingent on repentance: "if your brother sins, reprove him, and if he repents, forgive him" (Luke 17:3). Notice that there are three conditions in view: (i) the offender is a "brother," a fellow Christian; (ii) the offender is penitent and contrite, and (iii) the offended party is forgiving the offender for a wrong done by the offender to the offended party. In other words, I can forgive Jim for what Jim did to me (personally), but I can't forgive Jim for what Jim did to John.
Many Christians are very confused about forgiveness because they don't study the details for themselves, but simply recite a popularized, sloganized sound-bite.
8. Regarding the Sermon on the Mount (Matthew 5-7), several things need to be said:
i) This is not dealing with genocide or crimes of violence. Rather, it is dealing with personal affronts and civil infractions.
ii) There is a radical element to the Sermon on the Mount. Instead of simply reacting in kind, we should restrain our punitive impulses and be merciful, acting in the best interests of the offender. We should return good for evil, rather than evil for evil. We do not become the thing we hate. We do not model our code of conduct on the enemy.
One presupposition of Christian ethics is that a Christian has a limited stake in this world. Another presupposition is that we are all sinners, and those of us who have been redeemed should try, where possible, to redirect other sinners in the way of righteousness, blessing them as the Lord has blessed us--showing mercy because the Lord has shown us mercy.
iii) However, the Bible is not all about doing mercy; the Bible is also about doing justly. We can't be equally loving to everyone. We can't be merciful to the merciless without being merciless to their victims. There are certain moral and practical priorities.
P.S. I hope you don't receive any hate-mail for your article on hatred! :-)