We’re have on our hands this awkwardly uncomfortable situation: we’d often like to be Marcionists (that is, drop the Old Testament), but truth compels us to keep the Old Testament in some way – ah, and these very terms ‘Old Testament’ and ‘New Testament’ were invented by the heresiarch Marcion. As for the New Testament, we see it as more discontinuous with the Old Testament than continuous, and thus the Old Testament sometimes seems more than anything to be a foil to the New, not the revelation that Christ and his way fulfil.
Hermeneutically, as we often see it, Christ fulfils some prophecies in Scripture, and then in some vague sense his Passion ‘fulfils’ the Old Testament in a grand wash-out that erases every theological importance of the sacrifices ordered in the Law of Moses except for their inconvenience – because God forbid that humanity keep having to do such inconvenient things as sacrifices when it’s all really just a matter of the heart (since our hearts are good and pure whenever we want to obey God). As I’ve said before, though, Jesus didn’t BS exegesis for the sake of teaching a true doctrine and a true life: even when his reading went far beyond the original human intent in the Scriptures, it was legitimate by more than divine fiat.
But statements made by Jesus and Paul, even about loving enemies, were truly rooted in the Old Testament, in the God who inspired the writing of its books: they were reading and rereading the Scripture in light of eschatological reality, and they were reading themselves by the words of Scripture. What about those parts that we’re tempted to excise and call inapplicable to the present age? The Old Testament teaches hatred because it teaches love. Though we dare not simply flatten the thought of the Old Testament books, we must come to grips with the fact that they testify about the Christ.