Habit forms from custom, and habit seems to accustom itself to nature. It is much worse and more difficult to change nature. However, with God it is possible. For nature does not set itself against God.
Not he is chaste in whom shameful thoughts stop in time of struggle, work and endeavor, but he who by the trueness of his heart makes chaste the vision of his mind not letting it stretch out towards unseemly thoughts.
The more wood you pile on a fire the more heat you get, and thus it is with God - the more you think on Him the more you are fired with love and fervor towards Him. He who loves the Lord is always mindful of Him, and remembrance of God begets prayer.
Be careful not to neglect the small things, take care not to despise them as something insignificant. They are not insignificant; they are cancer for the soul, a bad habit. Let us therefore be vigilant. Let us pay attention to slight things, whilst they are still slight and before they become serious. Both the life of holiness and the sinful life start from little things and lead to greater ones, either good or bad.
A wise elder gives the following advice to monks and youth alike: 'Avoid eating foods which are to your liking, but, preferably, eat the simplest foods, and be thankful to God, Who also sends you these.'
Train yourself to cut off an intrusive thought immediately…Be at pains over this, so that you acquire the habit. The soul is a creature of habit: according to the habit you have acquired, so will you act all the rest of your life.