It would just be a guess but I’d generally assume that the definition of “good” at the time was obeying the laws of the primary gods and “bad” was breaking those laws.
I also suspect that there were trickster and evil gods, who were little spoken of and rarely turned into statues. We see hints of them sometimes in the forms like the snake or as demons, etc. In general, these gods tried to convince people to break the laws.
But so, let’s say that someone asks you to explain the universe and you start by describing this great, all-powerful deities and how they have their laws… The person asks, “But, if they’re so powerful, how can it be that sometimes, people do break the laws?” They can’t be “all powerful” and also unable to prevent us from breaking the laws. That’s a contradiction.
Evil, trickster gods helps to explain this. There’s a battle/struggle going on and - even though the law gods are the more powerful - the trickster gods are able to corrupt people, every once in a while.
But then you have a second issue which is that humans are clearly different than animals. Animals just do what they’re told. Maybe they do something bad, but it’s because they were mislead and not because they intended to do wrong. They’re simple creatures. Humans are different and sometimes can and do choose to do wrong. Clearly, there’s something different about us, compared to animals.
Animals must be mislead into doing evil. Humans can and do choose to do evil, without outside prompting, sometimes.
Ergo, the fruit of the tree of knowledge. At one time, we were like animals - simply living like sheep in God’s garden. And, like animals, we were able to be mislead into bad behavior. But then we gained greater knowledge and were lifted above the other creatures. Among that knowledge, was a clear understanding of the laws and that one can choose to not obey the laws. Doing so is, effectively, working for the trickster deities, but it can be done.