6 Marcella then lived the ascetic life for many years, and found herself old before she bethought herself that she had once been young. She often quoted with approval Plato's saying that philosophy consists in meditating on death. A truth which our own apostle endorses when he says: “for your salvation I die daily.” Indeed according to the old copies our Lord himself says: “whosoever does not bear His cross daily and come after me cannot be my disciple.” Ages before, the Holy Spirit had said by the prophet: “for your sake are we killed all the day long: we are counted as sheep for the slaughter.” Many generations afterwards the words were spoken: “remember the end and you shall never do amiss,” as well as that precept of the eloquent satirist: “live with death in your mind; time flies; this say of mine is so much taken from it.” Well then, as I was saying, she passed her days and lived always in the thought that she must die. Her very clothing was such as to remind her of the tomb, and she presented herself as a living sacrifice, reasonable and acceptable, unto God.
Source: Letters (New Advent)