True happiness is found in unselfish love, a love which increases in proportion as it is shared. There is no end to the sharing of love, and, therefore, the potential happiness of such love is without limit. Infinite sharing is the law of God’s inner life. He has made the sharing of ourselves the law of our own being, so that it is in loving others that we best love ourselves. In disinterested activity we best fulfill our own capacities to act and be.
Yet there can never be happiness in compulsion. It is not enough for love to be shared: it must be shared freely. That is to say it must be given, not merely taken. Unselfish love that is poured out upon a selfish object does not bring perfect happiness: not because love requires a return or a reward for loving, but because it rests in the happiness of the beloved. And if the one loved receives love selfishly, the lover is not satisfied. He sees that his love has failed to make the beloved happy. It has not awakened his capacity for unselfish love.
Hence the paradox that unselfish love cannot rest perfectly except in a love that is perfectly reciprocated: because it knows that the only true peace is found in selfless love. Selfless love consents to be loved selflessly for the sake of the beloved. In so doing, it perfects itself.
The gift of love is the gift of the power and the capacity to love, and, therefore, to give love with full effect is also to receive it. So, love can only be kept by being given away, and it can only be given perfectly when it is also received.
-from No Man is an Island by Thomas Merton (pp. 19-20)