I like to imagine how a movie story can be explained, rationalized, etc. as a creative exercise of my own. So The Prophecy trilogy for me was a good one to work on.
How can G-d let an angel of all things go loose messing up His creation like that? Assumption: even angels have free will without which the whole fallen angel legend falls apart. They can disobey. They know right from wrong deep down, and do something in accordance or against it.
How can G-d let an angel who's done that come back? Assumption: G-d is endlessly forgiving and we all assume or hope for that in fear of what if he isn't. All that is needed is the true repentance that comes with knowing the truth, and then accepting it. It's a horribly short and insufficient way of putting it but I think you get what I'm saying.
Okay, so Gabriel does all that killing, and then comes back at the end to grace. In between is the lesson of how. He becomes arrogant as Lucifer says, and that's evil, and that's the devil's. He is punished in the usual way but is spat out because well, you've got two devils and that's one too many in Hell.
I learn from this that punishment does not bring the recognition of the truth, merely a desire to avoid punishment. Your actions may not violate, but your spirit does. If your spirit be right, then you need fear nothing for nothing would you do deserving of punishment.
His lesson is learned amongst humans after Michael takes away Gabriel's mark of G-d and this tells me symbolically that G-d can indeed remove your elevated status whatever you've achieved. Even an angel can be humbled. You too can, and it isn't actually that G-d does it, YOU do it to yourself by virtue of your actions having (somewhat predictable) outcomes.
(G-d's world is not perfect nor can it be for it to have meaning. There must be the simple adversity of unpredictability. In other words, bad shit happens to good people. However, if you knock over a vase onto the floor, it will probably hit the floor and break. Insult someone, and they will most likely be upset with you. Some things are deterministic. However, the interplay of deterministic events on a suitable scale is beyond computation and amounts to probabilistic chaos at best and this is where you have to try to follow the simple rules, pay attention to the little things, and feel your way through. If you need to hear this from me, you really didn't pay attention to Star Trek. It does point up though the saying in Hagakure that things of large importance should be taken lightly and things of small importance taken seriously.)
Among humans, he sees how they live and sees the desperation and hope they still manage to have despite that desperation. Like a child being taught to swim and being dared by an adult to strike out into the water and trust they won't be allowed to drown, G-d talks to us and we hear Him somewhere deep inside us across what seems like a vast gulf, and we strike out from the material everyday world of what we can hold on to and fearfully reach for G-d... who seems just out of reach. It's frightening. As Lucifer says, it's so hard to have faith...
Yet... we do. In some small way it is an act of hope to fill your car's gas tank because it implies you think you will be going somewhere. Not that you might, but that your estimation is that you are so likely to go somewhere as makes no difference between that and definitely going somewhere.
People rarely consider these things.
When I can get it together right, I will do a take on The Matrix trilogy.