When we sin, it is generally to satisfy the body craving for what it has not, or for that which is forbidden. Why did God leave this concupiscence in us? He left it, first, to keep us humble, by reminding us of our former sins, and, secondly, that we might overcome it and have a reward for the victory.
The second branch of the Church is called the Church Suffering. It is made up of all those who have gone through this world and are now in Purgatory.
Some of them while on earth fought well, but not as well as they could have done; they yielded to some temptations, fell into some small sins, received some slight wounds from their spiritual enemies, or they have not satisfied God entirely for the temporal guilt due to their great sins; therefore they are in Purgatory till they can be completely purified from all their sins and admitted into Heaven.
The last or third branch of the Church is called the Church Triumphant, and is made up of the angels and all those who have lived at one time upon earth and who are now in Heaven with God, enjoying their rewards for overcoming their spiritual enemies and serving God while upon earth. They are triumphant or rejoicing because they have reached their heavenly home.
You must not think that those only are saints who have been canonized by the Church and whose names are known to us; for all in Heaven are saints, as we also shall be if admitted into that happy eternity. God wishes all to be saints, for He wishes all to be saved. You know we can pray to the saints and ask their help and prayers; but how could we know that certain men or women are really in Heaven? We can know it when the Church canonizes them, and thus gives proof that they were great spiritual heroes in the service of God and can be more confidently appealed to on account of their eminent sanctity and powerful intercession.
Therefore the Church by canonization tells us for certain that such and such persons are truly in Heaven. But might not the Church be deceived like ourselves?
No! for Christ has promised to be always with His Church, and the Holy Ghost is ever directing her, so that she cannot err in faith or morals. If the Church made us pray to persons who are not saints, she would fall into the worst of errors, and Our Lord would have failed to keep His promise—a saying that would be blasphemous, for Christ, being God, is infinitely true and could not deceive or be deceived. To canonize, therefore, does not mean to make a saint, but to declare to the whole world that such a one was a saint while upon earth. After death we cannot merit, so our reward in Heaven will be just what we have secured up till the moment of our death; hence holiness is acquired in the Church Militant.
How does the Church canonize a saint? Let us suppose some good man dies, and all his neighbors talk about his holy fife, how much he did for the poor, how he prayed, fasted, and mortified himself. All these accounts of his life are collected and sent to Rome, to the Holy Father or to the cardinals appointed by him to examine such statements. These accounts must show that the good man practiced virtue in a more than ordinary manner, that he either performed some miracles while he lived, or that God granted miracles after his death through his intercession.