Every "good and perfect gift" comes from God and the world was good before sin entered it. I see the world with that perspective.
Ever wonder that what is good to me isn't necessarily good to you and vice-versa? Two Godly persons can be one thanking God and the other blaming the Devil over the very same event.
Perfection never existed, good doesn't exist without evil.
It would seem that "good" and "evil" (in a sense of "positive" and "negative" or even "creative" and "destructive") must exist for there to be one important third component - a choice. For there to be a choice those two opposites need to be equal in size, but then the paradox is, that having a choice tilts the table towards "positive" because having a choice is a "good" thing.
Thus choice is as far as creation can go in terms of growing its destructive part. Once the two parts are equal, the choice is born and the whole thing becomes again slightly more positive. It would oscillate around this boundary indefinitely.
To the question of where diseases come from, it becomes apparent, that they are simply a reflection of the choices between "creative" and "destructive" made along the way.
The paradox is essential to understanding our existence, because that's the thing that sets everything in motion. As paradox cannot settle either way, it must oscillate indefinitely and that makes it a perpetual push-pull engine of creation. That is why the nature of existence is vibratory, every little particle out there is always in motion. The whole Universe oscillates around the fringe of the paradox and what you see around you is a shape of that fringe.