It's not my particular interpretation, it's what the book says.
The OT laws weren't really draconian by the standards of the day -- for example, "An eye for an eye and a tooth for a tooth" was a movement toward justice and mercy, because in the culture if someone put out your eye, you could generally take his life. Then there's the directive that a wife can be divorced but there has to be a written statement; that actually gave women a legal status they didn't have.
Why did it have to be a gradual process? Well, why does getting to democracy, and -- more importantly -- to human rights have to be a gradual process for peoples? The answer to both is that human societies can only be changed so much, so fast.
Now the laws weren't arbitrary, they were an expression of who God is, to those people at that time, an expression of the reality He'd made. Their mere existence reflected a flaw in creation, put there by humans, a flaw that needed to be repaired. The (f)law demanded death, demanded not just in the sense of justice and retribution, but in the sense of what was needed to bridge the hole and mend it. But God could have killed humans for all eternity and what was needed/owed wouldn't have been satisfied -- and He didn't particularly care to do that, since it would have been a waste of the prime point of Creation in the first place. Further, since God was the one who'd left the door open to the possibility of that flaw (when He gave his creatures called humans free will), it was rather His job to fix it.
So what Jesus did was "take the rap" for all us offending law-breakers/flaw-makers, repaired the flaw (as evidenced by the Resurrection), and did it by taking the brunt of the damage (called "sin" in the general sense of Creation being fucked up) on Himself, God.
It wasn't a matter of "I made up laws, you broke them... oh, heck, I forgive you", but of a deep alteration in the nature of reality, it was a matter of needing... well, a sacrifice, in the old, old sense of something appropriate to fill a need, which as a living being loses its/his life in the process. So He wasn't trying to impress anybody; he was doing what needed to be done -- needed if God wanted to keep Creation, and not toss mankind on the garbage heap of non-reality (if that was even an option; I'm not certain God could have just scratched it all off and said, "Back to the drawing board", without failing to be God... but that gets deep and hairy).