It partially fills the desire of our incomplete, lonely hearts for completeness in another. Friendship brings out the best in a person through forgetfulness of self. Yet it is limited as one cannot give totally of oneself to another because one is not in complete possession of oneself. Friendships are the result of virtue. They are based on a goodness in oneself that another can love.
Friends come to discover the good in each other and the relationship grows.
When God becomes the object of one's friendship we call it charity. From God's point of view He does not need to discover the good in us to become friends with us. God creates the good that is in us. His friendship has a creative effect on us. It makes us good.