Man needs a saviour because he fell from perfection in the garden of Eden. Some writers, in order to justify God, paint a very black picture of man and heap up superlatives about how bad he is and how much he deserves to go to hell. But I think the main point is not so much that man is bad, but rather that God is good and that no man had the moral strength to attain the perfection that is required to dwell in God's presence, until the advent of Christ. With this theme in mind I will explain my interpretation of the Garden of Eden, and my theory of the nature of sin.
After the creation of everything, including man: God saw every thing that he had made, and, behold, it was very good. (Genesis 1:31) So every emotion in the heart of man must have been good. How then can there be evil. It is because the same action which in one situation is good, may in another situation be inappropriate. For example: rest is good but laziness is bad; marriage is good, but adultery is bad; earning money is good but stealing is bad. Because man is smart enough (or so he thinks) to think of bad ways to satisfy good desires, and because he does not always have the moral strength to resist, he sins.
Situations for inappropriate behaviour arise naturally; they are not specifically planned by God. For example, if our neighbour is rich, it is not because God is trying to tempt us to steal; it may simply be because God has blessed our neighbour. It is written: Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man. (James 1:13) It would be difficult to create a world where it was impossible for anyone to ever steal; and even more difficult still to create a world where the thought of stealing would not even occur to anyone.
Because inappropriate situations naturally occur, man needs the moral strength and will power to say, ‘No’. It is the weakness of man which causes him to fall or sin; sin being when we hurt God or our neighbour in our attempt to get what we want. When someone steals, what is happening is not so much that they are being tempted by the evil desire to steal, but rather they are yielding to the natural desire to increase possessions, because they do not have the moral strength to resist their impulses when the situation deems such impulses to be inappropriate.
There are two solutions to the problem of evil: one is complete ignorance of all means of evil behaviour; the other is moral strength combined with the understanding that evil is not in the final analysis beneficial. The former was the initial solution for Adam. The latter is the final solution for man in the new creation.
I think the saying, ‘A little knowledge is more dangerous than no knowledge at all’, best describes the fall in the garden of Eden. Complete knowledge would have taught Adam that God's ways were always best. But a little knowledge, that he would be momentarily better off if he could find alternative ways to misuse God's gifts, was all he could learn from the tree of the knowledge of good and evil. God knew that Adam did not have the moral strength or the wisdom to resist temptation, once Adam had discovered it. Therefore God said to Adam: Of every tree of the garden thou mayest freely eat: but of the tree of the knowledge of good and evil thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die. (Genesis 2:16,17)
Eating of the tree of the knowledge of good and evil was the decision to learn independently from God. Adam gained the wisdom which: descendeth not from above, but is earthly, sensual, devilish. (James 3:15) This wisdom is characterised by: selfish ambition. (James 3:16 NASB) As a result of seeking this wisdom Adam and Eve were driven out of the garden, their bodies became subject to sickness and they eventually died. Furthermore, when they died they could not go to heaven immediately.
Adam and mankind in general have been excluded from paradise until they overcome sin. To overcome sin requires not only moral strength, but also a more complete knowledge than that which Adam possessed. Part of the reason for our existence now is that we may learn to acquire these faculties in difficult circumstances, that they may be strongly established in our character by the time we get to heaven, when of course living righteously will be much easier.
Complete knowledge and moral strength rely on many concepts such as gratitude, love, conscience, patience, logic, humility, fairness. We learn such wisdom from Jesus Christ as we trust and rely on Him, and labour for Him. He says: Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. (Matthew 11:29) As we keep Christ's word our wisdom is perfected until we feel unrestricted even though we are restricted by God's commands, because we see that God's way of holiness is better than Satan's way of sin. This freedom is promised by Jesus as we read and keep His word. He said: If ye continue in my word, then are ye my disciples indeed; And ye shall know the truth, and the truth shall make you free. (John 8:31,32)
But being perfected in the future does not solve the problem of the past. All of us have used our wisdom and ignored God's wisdom, and as a result chosen sin. So we were all under the sentence of death and separation from God according to the word to Adam: In the day that thou eatest thereof thou shalt surely die. Perhaps this means that from the day you eat of this tree your death is certain.
Note that this law only refers to death, not to punishments after death, which, although they occur for some, are not the subject of this law for all who sin. However, it seems that this law prevents sinners from going to heaven to enjoy eternal life. They must be separated from God.
I believe that the need to cancel this law of death and separation from God was the reason for the cross, and that punishments after death are irrelevant to the purpose of the cross.