The problem here is that the "central message" of Christianity, or any religion for that matter, depends on the interpretation people give to their holy texts. I've read virtually all of the Old Testament, and I can honestly say that if there was a "central message" to it, it was that the only reasons humans existed was to obey YHWH slavishly and in every particular, and if they didn't, bad things would happen to them and their country. Oddly enough, at the hands of invaders/conquerors (the Hittites, the Assyrians, the Babylonians, and the Romans), which weren't believers in the Jewish religion. Time and time again, Israel was conquered and the inhabitants enslaved, and by those who didn't believe in their god. In other words, YHWH was either not willing to lift a hand to spare his disobedient people from the horrors of being conquered, even when it meant that they were exiled from their promised land, or he actively connived to cause the invasions.
I suppose you can call that a relationship. You can also call a person living with an abusive spouse a relationship. Doesn't mean I'd want a part of either one.