In order to be canonized a saint, the Church must determine that the individual practiced "heroic virtue."
The road to becoming a canonized saint is often a long one, taking many years and sometimes even centuries.
However, before an individual can be considered, the Vatican must confirm that the man or woman lived a life of “heroic virtue.“
What does “heroic virtue” mean?
The Catechism of the Catholic Church offers a brief explanation behind the Church’s canonization process.
By canonizing some of the faithful, i.e., by solemnly proclaiming that they practiced heroic virtue and lived in fidelity to God’s grace, the Church recognizes the power of the Spirit of holiness within her and sustains the hope of believers by proposing the saints to them as models and intercessors.CCC 828
This brief summary notes that the canonization process recognizes the holiness of the person’s life and seeks to hold them up as models. The Church evaluates the life of the individual and sees in them an example for all to follow.
It’s an important qualification, as all saints were human and made mistakes in their lives. Living a life of “heroic virtue” does not mean they were free from sin. However, it does mean that they were able to overcome their weaknesses and live virtuously.
The Vatican has additional qualifications in its instruction for the process of evaluating an individual proposed for canonization.
The cause of beatification and canonization regards a Catholic who in life, in death and after death has enjoyed a reputation of holiness by living all the Christian virtues in an heroic manner … The reputation of holiness is the opinion that has spread among the faithful about the purity and integrity of life of the Servant of God and about the virtues practiced by him to an heroic degree.
After the death of an individual, this requires interviews with friends and family members, where they must list “specific examples of the exercise of the individual virtues.”
As each person is unique, the Vatican never goes into great detail regarding the specific virtues that qualify a saint. It is up to the researchers to determine if an individual lived heroically, considering the totality of their life and the context of their reputation of holiness.
It all goes back to the previous note of the Catechism that these people are to be held-up as models. If they did not have a reputation of holiness during their life on earth, then it is unlikely that they will be lifted up as a model for all to imitate.