"You're no saint," is a common (if sort of mean) expression that fails to take into account how hard it actually is to become a real, Catholic saint. How canonization works has, understandably, gone through a few changes since the early days of the Church, but the rigour with which it's carried out has always been central to the process. Here, we'll walk through how one becomes a saint today — just in case that's in your 10-year plan.
Canonization itself can get a little complicated, but where it starts is simple. In order to be considered for sainthood, you must have died at least five years ago and either have a claim to martyrdom (like Saint Joan of Arc) or have performed a miracle.
Of course, acts of martyrdom and miracles come in many forms. Luckily, the Church uses a pretty simple rule to determine whether those acts are saintly or not.
Simply put, anyone who spends their life emulating Jesus and his teachings deserves to be canonized. In other words, a saint is someone who lived with "heroic virtue" and is definitely, absolutely with God in death. This is the first thing that the Church will check before even thinking about moving toward canonization.
This holiness is determined through a rigourous vetting process, in which the potential saint's records, writings, and life are analysed for anything that could be deemed impure — in other words, anything that goes against the values of Christianity. (It's kind of like the Christian version of combing through years of a new SNL cast member's tweets for anything offensive.) Once this person's life has been cleared of possible heresy, their case is sent to the Congregation for the Causes of the Saints.
The Congregation is responsible for taking an even deeper dive into the candidate's life as a Christian: What, specifically, did they do to prove their devotion to God? Were they committed to charity work? Did they serve their church with love and complete faith? This part of the process is equal parts research and discussion, as officials work together to determine whether this person was truly holy (and, until 1983, one official would be assigned the role of the "Devil's advocate," whose duty was to question and argue against the candidate's case).
The Congregation and other Vatican officials reach the end of their investigation when they can identify what, if any, miraculous acts this person performed in their life. According to PBS's Religion & Ethics Newsweekly, it's of the utmost importance to prove that an actual miracle took place. And all other explanations need to be ruled out before an act can be confirmed as a true "miracle." In one case, the Church actually sent for medical records to verify that the candidate healed someone.
If the Congregation finds substantial proof that the potential saint performed at least two miracles, it passes their case on to the Pope. It's up to him to make the final decision as to whether the candidate becomes a saint. Once the person is canonized, the Pope leads a special mass and their name is added to the official canon of recognized saints.
So, it's safe to say that, if someone achieves the title of "saint," their faith has been more than tested — it's been researched, questioned, and formally approved.