The event of falling in love is of such a nature that we are right to reject as intolerable the idea that it should be transitory. In one high bound it has overleaped the massive of our selfhood; it has made appetite itself altruistic, tossed personal happiness aside as a triviality and planted the interests of another in the centre of our being. Spontaneously and without effort we have fulfilled the law (towards one person) by loving our neighbour as ourselves. It is an image, a foretaste, of what we must become to all if Love Himself rules in us without a rival. It is even (well used) a preparation for that.
The basic principle of altruism is that man has no right to exist for his own sake, that service to others is the only justification of his existence, and that self-sacrifice is his highest moral duty, virtue and value. Do not confuse altruism with kindness, good will or respect for the rights of others. These are not primaries, but consequences, which, in fact, altruism makes impossible. The irreducible primary of altruism, the basic absolute, is self-sacrifice - which means: self-immolation, self-abnegation, self-denial, self-destruction - which means: the self as a standard of evil, the selfless as a standard of the good.