Initially the Church didn’t have a formal canonization process, but they held up for veneration men and women who were saintly examples during their life and at the moment of their death.
These “saints” were later categorized into two primary groups, into which all saints are separated. The categories hinge on the way the person died and how closely they imitated Jesus’ death on the cross.
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The saint-makers: Why did Popes John Paul II, Benedict and Francis canonize so many saints?
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A visual guide to 3 types of Christian martyrdom