From C. S. Lewis in Mere Christianity:
Faith, in the sense in which I am here using the word, is the art of holding on to things your reason has once accepted, in spite of your changing moods. For moods will change, whatever view your reason takes. I know that by experience. Now that I am a Christian I do have moods in which the whole thing looks very improbable; but when I was an atheist I had moods in which Christianity looked terribly probable. This rebellion of your moods against your real self is going to come either way.
That is why Faith is such a necessary virtue. Unless you teach your moods ‘where they get off’, you can never be either a sound Christian or even a sound atheist, but just a creature dithering to and fro, with its beliefs really dependent on the weather and the state of its digestion. Consequently one must train the habit of Faith.
The first step is to recognize the fact that your moods change. The next is to make sure that, if you have once accepted Christianity, then some of its main doctrines shall be deliberately held before your mind for some time every day. That is why daily prayers and religious readings and churchgoing are necessary parts of the Christian life. We have to be continually reminded of what we believe. Neither this belief nor any other will automatically remain alive in the mind. It must be fed. And as a matter of fact, if you examined a hundred people who had lost their faith in Christianity, I wonder how many of them would turn out to have been reasoned out of it by honest argument? Do not most people simply drift away?
Hebrews 2:1 — We must pay more careful attention, therefore, to what we have heard, so that we do not drift away. (NIV)
I Timothy 4:7-8 — Have nothing to do with godless myths and old wives’ tales; rather, train yourself to be godly. For physical training is of some value, but godliness has value for all things, holding promise for both the present life and the life to come. (NIV)
II Timothy 3:14-17 — …Continue in what you have learned and have become convinced of, because you know those from whom you learned it, and how from infancy you have known the holy Scriptures, which are able to make you wise for salvation through faith in Christ Jesus. All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the man of God may be thoroughly equipped for every good work. (NIV)
Grant us, Lord, we beseech thee, not to mind earthly things, but to seek things heavenly; so that though we are set among scenes that pass away, our heart and affection may steadfastly cleave to the things that endure forever; through Jesus Christ our Lord. Amen. –Leonine Sacramentary