The Enchiridion by St. Augustine
Chapter 3.--God is to Be Worshipped Through Faith, Hope, and Love.
Now if I should answer, that God is to be worshipped with faith, hope, and love, you will at once say that this answer is too brief, and will ask me briefly to unfold the objects of each of these three graces, viz., what we are to believe, what we are to hope for, and what we are to love. And when I have done this, you will have an answer to all the questions you asked in your letter. If you have kept a copy of your letter, you can easily turn it up and read it over again: if you have not, you will have no difficulty in recalling it when I refresh your memory.