Again, I see you being very vague here and not completely coherent. Too many answers? Are they all conflicting? If not, why shouldn't there only be one?
So, are you trying to establish an "answer" that Hinduism may not give, but that Christianity can? Alright then, here Hinduism, as far as I can tell, has an answer which is based on human nature.
The division into four classes is something not peculiar to Hindus only but is also seen in medieval Europe with serfs, merchants, kings/vassals, and of course priests/scholars. Some people have natural tendencies which fit more or less into one of these groups: not always completely of course, but reality never matches one's expectations exactly.
If you are good with high objects of thought, and you are intellectually/spiritually inclined, you are more of a Brahmana. If you are more of an administrator, or have a knack for working with people in projects and tasks, then you are a Kshatriya or governmental person. If you are good with money and business, or maybe you are an artisinal person, you would be a Vaishya, and if you are not intellectually inclined but simply like working with your hands, then you are a proud Sudra. Where do you fit in if not into one of these groups?
So the answer seems to be: human nature typically falls into one of these groups or is more or less situated in one of these classes.