What Defines Good & Evil
All things good are reflected qualities of the Most High. As beings embody and share those qualities, they are filled with light and made holy. As beings reject those qualities, their absence creates a void of light, which is darkness. This is not to say that a being can simply do good things and thus become holy. These qualities are not just characteristics the Most High possesses, but it is in him that the concepts find their definition. Therefore, they must be gained through relationship with the Most High.
Humans have been immersed in a corrupt reality and often have fickle or self-serving hearts. They must struggle in this world or they will tend toward darkness and it will become their ultimate end. They must seek and embrace the source of light. The elohim also face temptation to become corrupt, but without the same natural inclination toward corruption. However, elohim have witnessed the full glory of the Most High and when they choose rebellion, there is no path for them to come back. They are irredeemable.
When it comes to the terms good and evil, the scriptural use is different than you may think. It is better to think of the terms as beneficial and harmful. So, when a scripture speaks of bringing evil upon someone, it is speaking of bringing them harm.
Three Pictures of Nothingness
In the scriptures, it is described that the Most High created everything, but that picture may not be readily clear. There are actually three things mentioned as if they were already present - Darkness, The Deep, and the Barren Wilderness. While these are talked about as if they are something, think of them as nothing, the lack or absence of something - cold darkness being the absence of light, chaotic waters being the absence of order, dry barren wilderness being the absence of life. On the first three days of creation, the Most High addressed each of these. On day 1, he created Light. On day 2, he created Order. On day 3, he created Life.
As created being rebel against their creator, they become agents of de-creation. They bring about lifeless ruin, they live in darkness, and they tear down order into chaos. These images are embodied more directly in the bestial elohim and especially their chiefs - Leviathan (chaos), Behemoth (lifeless ruin), Ziz (darkness).