I will explain and it will be long, but it will give you the answer you are looking for you, even if you don't like it. I'm not telling you to believe this, I'm just giving you the answer that I feel accurately answers your questions, based on MY relationship with God and MY study of Scripture.
God created man with a Divine purpose. We were meant for so much more than this fractured earth. Things you can't imagine. We're here for now though, and this earth is destined to fail. That's why the world is slowly getting worse and worse, approaching a foretold(in scripture) end.
God's original plan for us was disrupted by his favorite angel Lucifer who, despite being blessed with unimaginable knowledge, power, fulfillment etc., wasn't satisfied and wanted to instead be God. God gave us all free will. He doesn't force us to obey Him. He is the epitome of reasonable. Lucifer chose to betray God though, the One who created everything and gave him everything(except being God Himself). Imagine the worst betrayal that a child could do to their parent here on earth, then multiply that by a thousand thousands, that's what Lucifer did to God.
Lucifer put together an army consisting of a (estimated) 3rd of the angels. Keep in mind that Lucifer was incredibly persuasive, and those angels had free will. Lucifer was no match for God's power though, and he was cast out of heaven onto earth. Lucifer becomes Satan (Hebrew for "an adversary, one who resists").
Before I continue, I must explain that while God is with us, in the Holy Spirit, here on earth, we are not in His presence. God, Jesus, Holy Spirit (Holy Trinity). God is in Heaven, Jesus(God in the flesh) came and died for our sins and now lives with us in the Holy Spirit(God in the spirit).
Once Satan was on earth he tempted Adam and Eve, causing the fall of man. Not only did God's favorite angel and a 3rd of his other angels betray Him, but his newest creation (man) had betrayed Him too. As a result, God decided to give Satan and mankind what they were asking for. They wanted to disobey God (who can only do good) and try to live without Him, so He showed them what it would be like. In comes the world, the broken earth, that we currently live in.
We live on an earth that is destined to fail, and Satan is destined to fail. While we are subjected to this failing earth, this earth that is full of evil and deception(from Satan), we are not destined for it. God clearly states that if we have faith, we will have salvation. Having faith means accepting that God sent himself in the flesh (Jesus) to die for our sins, so that we may not have to suffer what Satan and the followers of the world will have to suffer-which is seizing to exist. No fire and brimstone, DEATH. Death of your soul because you chose to not be with the One who created you, who gives you life.
As for people who were never exposed to Christianity, they need not worry. God is the epitome of fair. He sees the intentions of our hearts and He knows our ways. If they truly were never given a chance to know Him, He will give them a chance.
in conclusion, we have free will and we are not destined for this earth. God gaves us what we chose: a life without Him and full of sin. Now He has given us another chance to be with Him, so that we can get back to His original plan for us. An unimaginable eternity of power, knowledge, fulfillment, learning, pleasure, etc.