Let’s start by defining the word ‘sin’. Sin literally means ‘to miss the mark’. To miss the mark of what? The mark of perfection. So sin is imperfection. Since none of us are perfect, we’re all sinners. But imperfect compared to who or what? Compared to God who is perfect (Deuteronomy 32:4).
God’s core nature is holy and pure. He cannot be in relationship with sin in any manner (Habakkuk 1:13). To do so would be to violate the very essence of who He is.
God is merciful & loving but also just. Our sins are like crimes to Him and crimes must be punished. How would you like to live in a society where rape is excused or tolerated? Wouldn’t you rather live in a society where justice prevailed? Where these acts were dealt with and you could feel safe walking the streets?
The solution lies in a combination of God’s loving mercy and His perfect justice. Mercy cannot overlook or forgive sin without it being dealt with. Unfortunately, sin never stays the same or gets less. It always gets worse, it naturally spreads 1st Corinthians 5:6 says a little leaven leavens the whole loaf. If God were tolerant of our sin, heaven would be no better than life on Earth. And since sin always increases, in eternity heaven would be much worse than Earth is now. It is God’s just nature that sin be separated from purity, that wrongs be righted and that evil be vanquished.
Since we, being sinners, cannot pay for our own sins, God Himself came down to Earth, lived a perfect life and paid for our sins Himself. As long as we realize it by giving our lives over to Him, His justice and mercy are both satisfied (Romans 3:24,25 & 6:23, 1st John 5:11-13). By giving our lives over to Him now, when we die He will take away our sin nature completely. He will not have violated our free will, yet heaven’s purity will be maintained and we can have fellowship with Him for an eternity (Micah 6:8).
Those who do not accept His offer of forgiveness will have to pay the penalty for sin themselves. The Bible says that payment is spiritual death…separation from God forever (Romans 6:23 & Revelation 20:14,15). By their own choice, they will have rejected God. They don’t want to be in His presence for all eternity and He will honor that request.
All this is why God cannot tolerate sin.
“77 FAQ’s about God and the Bible” by Josh McDowell & Sean McDowell, page 56