4 The lesson also which was read today invites you to the true faith, by setting before you the way in which you also must please God: for it affirms that without faith it is impossible to please Him. For when will a man resolve to serve God, unless he believes that He is a giver of reward? When will a young woman choose a virgin life, or a young man live soberly, if they believe not that for chastity there is a crown that fades not away? Faith is an eye that enlightens every conscience, and imparts understanding; for the Prophet says, And if you believe not, you shall not understand.
Faith stops the mouths of lions, as in Daniel's case: for the Scripture says concerning him, that Daniel was brought up out of the den, and no manner of hurt was found upon him, because he believed in his God. Is there anything more fearful than the devil? Yet even against him we have no other shield than faith, an impalpable buckler against an unseen foe. For he sends forth various arrows, and shoots down in the dark night those that watch not; but, since the enemy is unseen, we have faith as our strong armour, according to the saying of the Apostle, In all things taking the shield of faith, wherewith you shall be able to quench all the fiery darts of the wicked one. A fiery dart of desire of base indulgence is often cast forth from the devil: but faith, suggesting a picture of the judgment, cools down the mind, and quenches the dart.
Source: Catechetical Lectures (New Advent)