LXII. To Him Who Wishes for Martyrdom.
Since, O son, you desire martyrdom, hear. Be as Abel was, or as Isaac himself, or Stephen, who chose for himself on the way the righteous life. You indeed desire that which is a matter suited for the blessed. First of all, overcome the evil one with your good acts by living well; and when He your King shall see you, be secure. It is His own time, and we are living for both; so that if war fails, the martyrs shall go in peace. Many indeed err who say, With our blood we have overcome the wicked one; and if he remains, they are unwilling to overcome. He perishes by lying in wait, and the wicked thus feels it; but he that is lawful does not feel the punishments applied. With exclamation and with eagerness beat your breast with your fists. Even now, if you have conquered by good deeds, you are a martyr in Him. You, therefore, who seekest to extol martyrdom with your word, in peace clothe yourself with good deeds, and be secure.
Source: Writings (New Advent)