The marks of the Church are necessary also because the Church must be a visible Church, that all men may be able to see and know it; for Our Lord said, "He that will not hear the Church, let him be to thee as the heathen and the publican." (Matt. 18:17). Heathens were those who worshipped false gods. Publicans were men who gathered the taxes from the Jews for the Romans; they were generally very cruel to the people, and were much hated and despised by them. Therefore Our Lord meant: if anyone will not obey the Church, you should avoid him as you avoid the heathens and the publicans, whom you despise. Now no one can be blamed for not obeying a church that is invisible and unknown. Therefore the true Church must be a visible body and easily known to all who earnestly seek it as the Church of Christ. But if some shut their eyes and refuse to look at the light of truth, ignorance will not excuse them; they must be blamed and fall under the sentence of Our Lord. *134 Q. From whom does the Church derive its undying life and infallible authority? A. The Church derives its undying life and infallible authority from the Holy Ghost, the spirit of truth, who abides with it forever. *135 Q. By whom is the Church made and kept One, Holy, and Catholic? A. The Church is made and kept One, Holy, and Catholic by the Holy Ghost, the spirit of love and holiness, who unites and sanctifies its members throughout the world. Lesson 13 ON THE SACRAMENTS IN GENERAL This lesson does not speak of any Sacrament in particular, but upon all the Sacraments taken together. It explains what we find in all the Sacraments. 136 Q. What is a Sacrament? A. A Sacrament is an outward sign instituted by Christ to give grace. Three things are necessary to make a Sacrament. There must be: (1) "An outward," that is, a visible, "sign"; (2) this sign must have been instituted or given by Our Lord; (3) it must give grace. Now, a sign is that which tells us that something else exists. Smoke indicates the presence of fire.