The Problem of Evil… is realistically too big a topic to tackle in what is essentially a blog post, but let’s take a (mercifully brief) shot at it. Basically, the question is why a good/ providential God permits evil to happen, whether to good people, or just in general(?). Theodicies (from the Greek meaning “vindication of God”) are attempts to explain this. You can go down several different rabbit holes on this particular topic, but for the purposes of brevity, we’ll just look at a couple of the Orthodox options. St. Irenaeus, writing in the 3rd century, had an interesting, if a bit unsatisfying explanation, based on our human free will, but predicated in our having been made in the image of God (imago dei). Because we’re made in the image of God we have the potential to achieve moral perfection, but we have to experience suffering (by means of evil) to develop ourselves as moral agents - basically, we become good through the experience of evil and suffering, which by extension is (if you’ll pardon the pun) necessary.
Blessed Augustine of Hippo, writing around the fall of the Western Roman Empire argued that as God is good, all things created by God are good, or at least begin as such. Because we’re not perfectly good (as God is), we are subject to temptation and our goodness is subject to degradation… through sin. A good way to think of it is a hole in a shirt, rot in a tree, blindness in an eye, etc. - all started out fine, but degraded over time. Another take (stick with me here) is to view it from the perspective of physics’ definition of “cold” - there’s no such thing, only an absence of heat; the further you get from the heatsource, the colder you perceive it to be. In an Augustinian light, the further you move away from God, i.e., the source of all goodness, the more evil/ sinful you will be. I rather like this one, even if I take issue with Bl. Augustine in several other areas, but more on him another time.