1 John 3:16

Hereby we know the love of God, because He laid down His life for us: and we ought to lay down our lives for the brethren. S. John here goes back to the law and living pattern of perfect charity, even Christ, who by laying down His life for us, taught us in like manner to lay down our lives for the brethren. For in Him there shone forth that boundless love which far exceeds the love of all parents and kinsfolk. For He, the Infinite God, laid down His life for us unworthy and ungrateful sinners, with great suffering and shame to Himself, and thus tacitly gave us a pattern for us to imitate, by laying down our lives for the brethren.

But yet we must not risk our own salvation in order to save the souls of others, though we are bound to risk our life for their salvation, which is of more value than our own earthly life, which we must undoubtedly sacrifice for the eternal good of others, as S. Paul did and the other martyrs.

But you will ask, are we bound to risk our own lives for the sake of the lives of others? In ordinary cases, No, but in extraordinary cases, Yes. As when bound by oath or promise, or in defence of our country. But a friend is not bound to risk his own life for that of his friend, since that would be to love his neighbour even more than himself, which, S. Augustine says (de Mend. cap. 10), goes beyond the rule laid down. But yet to do so would be laudable, for a man would risk his life for the sake of honour, and for the virtue of friendship. And this is a spiritual good, higher than life itself. So S. Augustine teaches (de Amic. cap. 10); and S. Jerome on Micah vii. says, "When a man was asked, What is a friend? he replied, 'A second self.' And accordingly two Pythagoreans gave themselves up to the tyrant as mutual pledges for each other." (See S. Ambrose, Off. lib. iii.; Fr. Victoria, Relect. de Homicid.; Soto, de Just. i. 6; and S. Thomas, 2. 2, q. 26, art. 4, ad 2). And Valentia adds this case, "Ought a man to suffer himself to be killed rather than kill his assailant?" And he rules that he ought rather to be killed himself, than kill another who would die in the very act of sin. We should also risk our life to preserve another's chastity. As the soldier who saved Theodora by changing clothes with her in prison, and who in the end suffered with her. And Paulinus, who became a slave in the place of a widow's son (slavery being a kind of civil death), and who was highly praised for his act by S. Augustine and other fathers.

Instances are also given from heathen authors of those who gave up their lives for their friends, which is the highest proof of love. See John 15:13.