Great artists and poets have caught this acme of human existence. Shakespeare captured this in his sonnet 116:
…Love is not love
which alters when it alteration finds…
Love alters not with his brief hours and weeks,
but bears it out even to the edge of doom.
If this be error and upon me prov’d,
I never writ, nor no man ever lov’d.
Parents and siblings will give their lives for one another; patriots will die for their nation. Biology and social order have been proposed as the root of such deeds. Yet when people risk their lives for a stranger, an enemy or even for a deeply embraced conviction, such explanations ring hollow.
Source: Catholic DiscoveryAbout Faith