OLD TESTAMENT means "Old Covenant," which means the old agreement that was arrived at between God and Israel at Mt. Sinai with Moses presiding. "I shall be your God and you shall be my people" (Leviticus 26:12) sums it up—that is, if you obey God's commandments, God will love you.
New Testament means "New Covenant," which means the new agreement that was arrived at by God alone in an upstairs room in Jerusalem with Jesus presiding. Jesus sums it up by raising his wine and saying, "This cup is the new covenant in my blood" (1 Corinthians 11:25).
Like Moses, Jesus believed that if you obey God, God will love you, but here he is saying something beyond that. He is saying if you don't obey God, that doesn't mean that God won't love you. It means simply that God's love becomes a suffering love: a love that suffers because it is not reciprocated, a love that suffers because we who are loved suffer and suffer precisely in our failure to reciprocate. By giving us the cup to drink, Jesus is saying that in loving us God "bleeds" for us—not "even though" we don't give a damn, but precisely because we don't. God keeps his part of the covenant whether we keep our part or not; it's just that one way costs him more.
This idea that God loves people whether or not they give a damn isn't new. In the Old Testament book of Hosea, for instance, the prophet portrays God as lashing out at the Israelites for their disobedience and saying that by all rights they should be wiped off the face of the earth, but then adding, "How can I hand you over, O Israel? . . . My heart recoils within me . . . . I will not execute my fierce anger . . . for I am God and not man, the Holy One in your midst, and I will not come to destroy" (Hosea 11:8-9).
What is new about the New Covenant, therefore, is not the idea that God loves the world enough to bleed for it, but the claim that here he is actually putting his money where his mouth is. Like a father saying about his sick child, "I'd do anything to make you well," God finally calls his own bluff and does it. Jesus Christ is what God does, and the cross where God did it is the central symbol of New Covenant faith.
So what? Does the suffering of the father for the sick child make the sick child well? In the last analysis, we each have to answer for ourselves.
Like the elderly Christ Church don who was heard muttering over his chop at high table, "This mutton is as hard to swallow as the Lamb of God," there are some who find the whole idea simply unswallowable—just the idea of God, let alone the idea of God in Christ submitting to the cross for love's sake. Yet down through the centuries there have been others—good ones and bad ones, bright ones and stupid ones—who with varying degrees of difficulty have been able to swallow it and have claimed that what they swallowed made the difference between life and death.
Such people would also tend to claim that, whereas to respond to the Old Covenant is to become righteous, to respond to the New Covenant is to become new. The proof, they might add, is in the pudding.