There’s sanctification, and then there’s being an actual saint.
Many of us probably associate that term with Catholicism, and for good reason. In the West, that term specifically originates with the Roman church, before many Protestant denominations shed it in the course of schisming from their historical roots. The Catholic Church isn’t the only branch of Christianity to recognize saints, though: the concept also plays a role in Lutheran, Anglican, Eastern Orthodox, and Oriental Orthodox theology.
And like many terms we use in discussing culture, we often broaden the sense of “saint” to refer to similar-but-different concepts in other religions. Many faiths recognize individuals who were particularly holy in life — or are particularly holy, though I believe veneration of living saints is substantially less common. This idea crops up, in a variety of forms, in Judaism, Islam, and the various Indian religions. Arguably it even appears in Shintō, when the kami in question is the spirit of a deceased person . . . though it’s interesting to note that one of the more well-known examples of that is Sugawara no Michizane, who was deified as Tenjin after his vengeful ghost brought calamity upon the imperial capital. Normally we think of saints as being more benevolent!
In using this term more broadly, we have to consider what qualifies someone for sainthood. How do we decide that it’s fair to refer to a bodhisattva or a rishi or some other non-Christian exemplar as a “saint”?
Probably people don’t agree on all the specific uses, but there is something of a framework to go by. A saint is often going to be a model of ethics — though this doesn’t preclude an unethical past; they just have to have set themself on the right path eventually. In many of the cases where we see saint-type figures, this frequently means they’re notably ascetic, since forgoing material comforts is admired and holy behavior in their religions. And it also means they tend to be noted as teachers, since sharing one’s wisdom with others is meritorious. They have a particular connection to the divine beyond what an ordinary person might possess, whether that be the enlightenment of a Buddhist arhat or bodhisattva or the intercessory capacity of a Christian saint . . . and because of that divine connection, they may have the power to work miracles.
What’s a miracle? At its core, it’s any inexplicable event attributed to supernatural causes. Specifically, though, we use it to mean beneficial events attributed to divine causes — the line between “magic” and “miracle” being fuzzy and dependent on one’s theological opinion of magic. For miracles to be attributed to a saint, we look for some kind of causal connection: you prayed to the saint and your incurable cancer went into remission. Without that link, the miracle is credited to the divine more generally. But while outsiders may see this as polytheism by a different name — pray to spiritual entity; spiritual entity provides miracle — in monotheistic faiths, the vital distinction is that the saint is interceding with God, improving the chance of the miracle occurring, rather than performing it with their own power.
How a person becomes a saint is really two questions: first, how one achieves that state of holiness, and second, how one comes to be recognized by the religious establishment as a saint. Where the first is concerned, the range of answers is wider than you may think! An Indian rishi may achieve insight into the cosmos through intense asceticism and meditation, while some views of Jewish tzadikim hold that their special status is bestowed by God and cannot be attained through personal effort, and in some forms of Christianity all souls in heaven are referred to as saints, albeit of a different sort than those capable of miracles. In Christianity especially, but also in Islam, martyrdom frequently plays a key role in the path to sainthood (especially in their early history), as the act of giving up one’s life for the faith is perhaps the ultimate expression of piety.
Recognition of sainthood is a separate matter, and some religions systematize this to a high degree. The history of the Catholic Church shows numerous changes to the process, generally aimed at greater centralized control; prior to the late tenth century, saints’ cults were entirely local and acknowledged by bishops, but by the late twelfth century only the Pope could canonize saints. Around the same time, I believe, saints were required to be dead before they could be canonized — no more living saints. Nowadays canonization is a multi-step process, with a candidate first being titled a Servant of God, then proclaimed as Venerable, then beatified (which ordinarily requires either martyrdom for the faith or one confirmed miracle), then finally canonized as a saint throughout the entire church.
By contrast, Islamic walī look more like early Christian saints, in that their status is assigned by popular acclaim rather than a central authority. Meanwhile, I believe most if not all rishis are well in the past — I don’t think it’s a title being bestowed today, though if I’m wrong, someone please correct me — and the Talmud says there are at least thirty-six tzadikim living at all times, but they are anonymous rather than individually identified and venerated. Such wide variety befits a situation where one term (“saint”) is being applied across many cultures and faiths.
When it comes to that idea of veneration, much of the relevant practice looks like the broader practice of the religion, with prayers and offerings like candles. Because saints were human beings, though, and some of them lived recently enough to be historically traceable, their tombs often become important sites of pilgrimage and prayer. Relics may also play a key part in this, whether they’re bodily items like hair and bone or important possessions the person used in life.
How this all fits into the faith can fluctuate over time. The Protestant Reformation led to a strong pushback against the idea of formally recognized saints who can intercede with God (as opposed to all the dead in Heaven being saints); modern revivalist movements such as Wahhabism are aiming for the same goal within Islam. Reforms within the Catholic Church removed a number of historically questionable saints from the General Roman Calendar — which has filtered out into the populace as those saints being “de-canonized,” though this is not an accurate description. But whatever the authorities might say, actual practice on the ground may differ, as the devotion of the people to these exemplary souls continues.