If you are asking what makes a canonized Saint, I usually hear it said that the Church recognizes what is already happening.
Typically, people who know the person in life will attest to their personal holiness. After death, local people who know them might ask their intercession, etc. If miraculous healing, etc. results from these requests for intercession, or are associated with relics, the Church investigates. And it may be that they decide to canonize the person.
The statement is usually that the person is one that God chooses to bestow His grace through (the healings, etc.) so it is God that "verifies" a Saint.
Of course, we are ALL called to be saints, and in the epistles, the members of the Church are addressed as such. The thing is, we don't speculate on the salvation of individuals. So unless God shows that He uses that person as a "vehicle" for grace, we don't have "proof" ... so everyone else remains not officially canonized. The vast majority of true Saints are known only to God.
Corrections welcome - this is what I have received from priests and various teaching podcasts.