Love as affection often happens without our will. People "fall in love".

As affection eventually diminishes staying in love must be worked at by both parties.

The person loving must encourage feelings of affection(work) and the person loved must behave in a fashion that encourages affection.(earn)

What begins as unintentional and automatic becomes intentional and deliberate.

This intentional and deliberate love is required of all Christians with all people; those they know and those they have never met.

What makes the Christian different from the rest is that he is required, by God, to love in this manner regardless of  the behavior of the person being loved.