Sin is the falling short of God's standard (a negative), not some [positive] "thing" that He must have created along with everything else. It's really not a duality. There's God's will, and there's other than God's will. Once God ordained a will, there was automatically the possibility of something else.
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"there was automatically the possibility of something else" ??
Where did sin come from?
Was it not in the creation of the will?
If it wasn't, then free will has no meaning. There would be no ability to do evil if evil was not an option.
It's not refusing to seek the answer. Because you too will reach a point where you will claim an answer can't be known. And that's when the reason God willed people to be lost is raised. Then, you, along with the Calvinists, pledge "his Higher purpose".
I already have my answer to this, God can and does seal a person's fate after much longsuffering, allowing them time to repent and choose. Again, it is both. God's will to give personal free will time to choose and then God's will to close that door and the invitation is void.
:jesus: