As the word "unreasonable" is open to misunderstanding, the matter may be more accurately put by saying that each one of these Christian or mystical virtues involves a paradox in its own nature, and that this is not true of any of of the typically pagan or rationalist virtues. Justice consists in finding out a certain thing due to a certain man and giving it to him. Temperance consists in finding out the proper limit of a particular indulgence and adhering to that. But charity means pardoning what is unpardonable, or it is no virtue at all. Hope means hoping when things are hopeless, or it is no virtue at all.And faith means believing the incredible, or it is no virtue at all.
G. K. Chesterton, 1874-1936, Heretics, Chapter Twelve, Paganism and Mr. Lowes Dickinson, (Barnes & Noble Inc., 2007, p. 83).
Are these virtues indeed paradoxical? How do we develop them?