Adam-Eve
Adam and Eve were created by God and placed into Eden, paradise. Eden was perfect and holy, without evil. They had fruits to eat from the trees and they were not ashamed of their nakedness. The walked with God, as they did not sin. Everything they they did was Good, thus aligned with God. Yet they broke the one and only rule given to them by God. Why?
Why did they eat the forbidden fruit? (the serpent) Why did they go against God? (they were deceived, tempted) Why was the serpent in the Garden? (God created it) Why did God give them the one rule? (the potential of evil) Why do we inherit original sin from them? Why do we deserve it? (natural consequence) Why did God curse the serpent? (the serpent is also a free agent) Why did God make pregnancies painful? () Why did God punish all of them? Adam, Eve and the serpent (all of them sinned) Where was Adam sent after getting kicked out of Eden? (Gen. 3:23)
When studying Adam and Eve, it is important to understand them and their state as being purely spiritual. The story makes it sound like they were physical beings and lived in a real physical garden, but to fully understand the significance of the narrative, we should treat every aspect of the story as an immaterial one.
For example, it makes sense to ask the question: "Why do we inherit the sin of Adam? We did nothing to deserve it, but now we must pay with our lives? That's unjust!" - Indeed, it would be unjust if we were to be punished for their physical action, the eating of the fruit. But that's not why we're being punished. Instead, our punishment is derived from their spiritual crime, that is, that they brought sin into the world. Before their sin, there was no sin. Everything was good, as God saw it. But Adam and Eve introduced sin into the world, and thus we inherit from them the poor spiritual state, not a physical one. Not only did Adam and Eve live in a different "physical" state (holy, perfect, Paradise), they also lived in a different spiritual state: they walked with God! Their sin deviated their path from God's path forever, and that is what we've inherited. We have become separated from God. And once their path separated from God's, God called out: "Where are you?". Their punishment was death, literally, as they would've lived in the Garden forever. But they were kicked out, and now all of our lives shall come to an end.
And we can understand that it's a larger step to go from nothing to something, than it is to go from something to something else. The sin of Adam made it so that instea the world having zero sin, there would now be some sin. And it's this sin, that we partake in. And so, it's not unjust that we inherit it. Instead, it's a reasonable consequence. Spiritual causes have spiritual effects. Material causes have material effects. Like a drug-abusing mother, whose children are born with birth-defects: the children are innocent, and did not deserve their physical state, but it is a natural consequence of their mother's actions. Similary, the natural consequence of not walking with God, not being in the Garden, is eventually, death. Because only in God is there life.
But if Adam and Eve walked with God, how did they manage to sin? Indeed, I would compare their state of spiritual ignorance to the physical addiction to a substance: You can't have a craving for heroin, if you've never had any. It's physically impossible. Similarly, Adam and Eve didn't have a craving for sin, for they were completely ignorant of evil. It was impossible for them to do evil, because they did not know of it. This is why there had to be an external source of evil, another person, the serpent. The serpent convinced Eve to eat the fruit, and Eve convinced Adam to eat some, too. Without the serpent, they would've never sinned.
So why did the serpent exist? I think this question might come back to Love. God wants us to choose Him. In order for us to choose God and love Him, we have to be free. Adam and Eve were free, clearly, as they had the ability to go against God. However, in order for us to be able to choose God, there must be some other option besides God. That is the role that the serpent fulfills. Adam and Eve were free creatures, but they didn't have any options to choose from. All they knew was the goodness of God, as they were ignorant of evil. The serpent provided them with that other option, that would lead them away from God. The tree of knowledge of Good and Evil was there even before the serpent tempted Eve, but they never even considered eating from the tree, as God had told them not to. Thus the serpent represents temptation, something that Adam and Eve did not experience before interacting with the serpent. This would imply that the rule ("do not eat the forbidden fruit") and temptation are two separate things, but both of them are required. This can be translated to: (potential for) evil and temptation (to do evil).
So temptation in the context of the Garden was another person telling falsehoods. Is this the definition of temptation? False ideas about something? Ideas that need to be externally introduced to? One could tell themselves falsehoods and tempt themselves?
Everything is under the control of God, and so we have reason to believe that the serpent was a part of God's plan all along. God created the serpent, after all. For us to love God, there must be temptation, so that we could truly choose God over the temptation. God created us good and holy, but we failed His test. And indeed, if Adam and Eve can fail to abstain from doing the one thing God specifically told them not to do, then we need not be too hard on ourselves, when we fail to love God, in our world of sin.
So what about the punishments? Why did God punish all of them: Adam, Eve and the serpent? The simple answer is that they all committed crimes against God. The serpent deceived Eve, and Adam and Eve ate the forbidden fruit. God is just, and thus they all must be punished.
But did the serpent have free will? If not, why did God punish the serpent? This gives room for the idea that the serpent was also a free agent. Perhaps the serpent was Lucifer aka. Satan, that God allowed and continues to allow to exist. If so, then Satan shall also be punished. Surely, one needs to have free will to be judged by God?
But did not the serpent introduce sin to the world first? The serpent was the one who deceived Eve. How is this resolved? An eternal enemy of God, Satan fills a strange role in allness. Satan is in complete opposition to God, and thus God doesn't need to tell Satan what is evil and what isn't. Did Satan pre-exist the physical world? Being an eternal enemy of God, Satan has already eternally made his decision about God, thus he doesn't need reminding of Goodness.
The story of the Garden is a direct parallel with the Christian notion of heaven. In heaven, we will have new physical bodies, yet be in close presence with God. Sin leads us away from God, and indeed, Adam and Eve were kicked out for a single sin, thus we have no chance to get into heaven, if we compare ourselves to Adam and Eve. This is why a divine sacrifice is required, so that we too can enter Eden, and ejoy everlasting life. For Adam and Eve had the tree of life in the Garden, from which they probably ate, granting them immortality. God calling out to Adam in the evening is a parallel to judgement day. God shall call everyone to Him and their sins shall be revealed. Adam and Eve even hear God walking, knowing of what is about to happen.
We learn that you shouldn't play with sin: commiting sin leads to more sin. We learn that sin has consequences. We learn that our free human nature is dangerous: even Adam and Eve were tempted to sin.