St. Ambrose having set forth the Virgin Mary as a pattern for life, adduces Thecla as a model for learning how to die. Thecla suffered not from the beasts to whom she was condemned, but on the contrary received from them signs of reverence. He then proceeds to introduce a more recent example.
19. Let, then, holy Mary instruct you in the discipline of life, and Thecla teach you how to be offered, for she, avoiding nuptial intercourse, and condemned through her husband's rage, changed even the disposition of wild beasts by their reverence for virginity. For being made ready for the wild beasts, when avoiding the gaze of men, she offered her vital parts to a fierce lion, caused those who had turned away their immodest looks to turn them back modestly.
20. The beast was to be seen lying on the ground, licking her feet, showing without a sound that it could not injure the sacred body of the virgin. So the beast reverenced his prey, and forgetful of his own nature, put on that nature which men had lost. One could see, as it were, by some transfusion of nature, men clothed with savageness, goading the beast to cruelty, and the beast kissing the feet of the virgin, teaching them what was due from men. Virginity has in itself so much that is admirable, that even lions admire it. Food did not induce them though kept without their meal; no impulse hurried them on when excited; anger did not exasperate them when stirred up, nor did their habits lead them blindly as they were wont, nor their own natural disposition possess them with fierceness. They set an example of piety when reverencing the martyr; and gave a lesson in favor of chastity when they did nothing but kiss the virgin's feet, with their eyes turned to the ground, as though through modesty, fearing that any male, even a beast, should see the virgin naked.
21. Some one will say: “Why have you brought forward the example of Mary, as if any one could be found to imitate the Lord's mother? And why that of Thecla, whom the Apostle of the Gentiles trained? Give us a teacher of our own sort if you wish for disciples.” I will, therefore, set before you a recent example of this sort, that you may understand that the Apostle is the teacher, not of one only, but of all.
Source: Concerning Virgins (New Advent)