The Enchiridion

You are anxious, you say, that I should write a sort of handbook for you, which you might always keep beside you, containing answers to the questions you put, viz.: what ought to be man's chief end in life; what he ought, in view of the various heresies, chiefly to avoid; to what extent religion is supported by reason; what there is in reason that lends no support to faith, when faith stands alone; what is the starting-point, what the goal, of religion; what is the sum of the whole body of doctrine; what is the sure and proper foundation of the catholic faith.

Now, undoubtedly, you will know the answers to all these questions, if you know thoroughly the proper objects of faith, hope, and love. For these must be the chief, nay, the exclusive objects of pursuit in religion. He who speaks against these is either a total stranger to the name of Christ, or is a heretic. These are to be defended by reason, which must have its starting-point either in the bodily senses or in the intuitions of the mind. And what we have neither had experience of through our bodily senses, nor have been able to reach through the intellect, must undoubtedly be believed on the testimony of those witnesses by whom the Scriptures, justly called divine, were written; and who by divine assistance were enabled, either through bodily sense or intellectual perception, to see or to foresee the things in question.