For one human being to love another human being: that is perhaps the most difficult task that has been entrusted to us, the ultimate task, the final test and proof, the work for which all other work is merely preparation . . . Loving does not at first mean merging, surrendering, and uniting with another person--it is a high inducement for the individual to ripen . . . to become world in himself for the sake of another person; it is a great, demanding claim on him, something that chooses him and calls him to vast distances.