Why did God create the idea of opposites? While I was finding out more about God, the ubiquitous question- did God create Hell? - often turned up. And many answers I have read mentioned that Hell was an inevitability due to the existence of Heaven; this is often paralleled by how darkness is a concomitant of light, and evil a concomitant of good. But where did this idea of oppposites even come from? Why did God who created this universe from a blank canvas decide that there must be opposites? It is as though he split up the canvas into half- one half for good and the other for evil. Isn't the idea of opposites a very 'human' concept?
In the vein of your question, I pose a simpler question whose answer may help us think about yours in the right frame of mind.

Does Good, by Definition, Require Evil in Order to Exist?

It is common for people have circular definitions for "good" and "evil." Evil is the opposite of good; good is the opposite of evil. In reality, the two are definitely playing for opposing teams, but they are not really opposites.

Evil definitely depends on good for its meaning. The converse is definitely not true, however. Good has meaning all on its own which does not depend on evil. In Genesis 1, after God creates the substance of the universe, he pronounces (nearly) each of these things "good." At this point, no evil has been mentioned, and by the end of creation, God pronounces the sum of his creation as "very good." Good seems to carry the meaning, "how God made it and intended it to be" or "according to God's will." Before chapter 3, the only thing that's spoken of as "not good" is a deficiency (something not yet created, woman) that God immediately remedies. There's no need for evil in this definition of good.

When sin and death enter the world, we see that evil is a corruption or perversion of good. Evil cannot be defined without their being good. Good has no such dependency.

Why did God Create (Moral) Opposites?

In a moral sense, I don't think you could say that there are opposites. There's what's good, which existed from the beginning of creation and would have remained even if humans had never sinned. Evil wasn't created by God. The capacity for evil was "created" because freedom is an essential element in genuine love, and for there to be freedom, the possibility of choosing something other than what was good was necessary.

God didn't create Heaven and Hell as two neighborhoods in the afterlife. In a metaphorical sense, Heaven is "intimacy with God" and Hell is "separation from God." Before Genesis 3, there was no need for Hell (for humans, anyway—little is said of the genesis of angels and daemons), and so it need not have existed as if God made it ahead of time knowing that he was going to need it eventually.

Moral "opposites" push you in opposite directions, but they are not, themselves, actual opposites.