Please explain the difference between a monk using a vow, a paladin using an oath, and a cleric gaining power though faith. Explain it to me like I'm a child.
I would prefer not to explain it to anyone like a child.
There is certainly overlap between all three terms, particularly given the often solemn, religious, or sacred nature that
faith,
oaths, and
vows often take. This should hardly be surprising considering that monks, paladins, and clerics have their roots in historical religions.
Nevertheless, there are distinctions, however fine or neglible one may think, between
oaths and
vows. As to the distinction between a "vow" and an "oath," this is a simple explanation that I found:
With the vow to accomplish something, a person dedicates himself to the task wholly. Whoever takes an oath to accomplish something is required to answer for it, for he has named himself or some one of his belongings as a pledge of his commitment and is thus bound by his very life, his honor, and his property.
Vows and oaths therefore affect a person's whole being; they put one's very existence in pawn. There is a distinct difference, however, between an oath and a vow: a vow is merely a personal promise, whereas an oath is a promise made before some institutional authority. In taking an oath, a person not only assumes an obligation but also becomes liable to prosecution; the state and society have an interest in his act. Oaths serve as objective guarantees of what is promised. Swearing to tell the truth, one guarantees that what one says is true. Oaths are self-endorsing.
The practice of oath taking by which a person places his very life at risk is an extremely ancient one. It is an institution of coercion, "the most powerful coercion known to primitive man" (Thurnwald, 1925, vol. 2, p. 39). Oaths are encountered among all peoples and in all cultures. They are a primal symbol of religion.
Because they are absolutely binding by nature, and because they are subject to both misuse and overuse, oaths are nevertheless looked upon with some suspicion in the fields of ethics, politics, and jurisprudence. They have to be judged in themselves, in relation to the particular substance of the promise they contain and the nature of the guarantee, as both tend to vary considerably depending on the level of the given culture and the conventions of the applicable code of law.
It's the reason why we don't talk of "monastic oaths" but, rather, of "
monastic vows." Vows are found across monastic traditions in Christianity, Hinduism, Jainism, and Buddhism. People already associate monks, in general, with the language of
vows. That's one reason why I personally IMHO like tying monks with "vows," something that reinforces the already present idea of "monastic traditions" that we see with the 5e monk.
This is a personal preference reflecting the whole "why/how would you rewrite the monk?" bit earlier. I personally would prefer the flavor monks shifted to either Vows or Psionics. With the former, it moves Monks closer to the religious sphere (e.g., Clerics, Paladins) whereas the latter moves Monks closer to the psionic sphere (e.g., Psions, Psychic Warrior, etc.).