Sin and death are extreme measures brought about by man's fall. Instead of glossing it over, the Bible shows how terrible the consequences of sin and death are. The question might better be - why did God decide to save mankind instead of destroy it completely. The first death is not the end according to the Bible. It is the second death that is to be feared. Nothing is lost to God who created all things.
The Old Testament was a shadow of things to come in the New Testament and symbolic in many ways, yet there still remains a final judgment of God against all evil. It is now put off by His grace until the final day of judgment, when all has been revealed on who will become sons of God and sons of the devil. Like the Old Testament children of Israel, we are to erradicate sin and evil from our lives much like the Israelites were told to destroy the wicked from the promised land they were given to possess. Because they so often did not obey God, those sins always would come back to haunt and hinder their lives. They would let evil kings live as slaves only to be enslaved by them later on by not obeying God's commandments. God's enemies were often given time to repent from sin, such as Nineveh. The stories are not always complete, resting on ones faith in God that He always does justly and will do no evil.
Understanding that all life belongs to God, to do with as He pleases, in perfect justice, is key to understanding and trusting that He is Creator; while we, the creature, have only the standing alloted to us by Him. We may think Him harsh, but we do not have the power to see the end of all things where each person is judged according to what they have been given in life by Him.
I believe nothing will ever be lost to unfair justice, but that all things will be done, ultimately, either accepting or refusing His great and awesome love.
...
