In words which can still bring tears to the eyes, St. Augustine describes the desolation in which the death of his friend Nebridius plunged him (Confessions IV, 10). Then he draws a moral. This is what comes, he says, of giving one's heart to anything but God. All human beings pass away. Do not let your happiness depend on something you may lose. If love is to be a blessing, not a misery, it must be for the only Beloved who will never pass away.
