Constant prayer protects against temptation, and unresisted habits strengthen over time.

Original passage

The temptations to which we are daily exposed make prayer a necessity. Dangers beset every path. Those who are seeking to rescue others from vice and ruin are especially exposed to temptation. In constant contact with evil, they need a strong hold upon God lest they themselves be corrupted. Short and decisive are the steps that lead men down from high and holy ground to a low level. In a moment decisions may be made that fix one's condition forever. One failure to overcome leaves the soul unguarded. One evil habit, if not firmly resisted, will strengthen into chains of steel, binding the whole man.