In this crowded world, with its intercourse and jostling, with its network of relationships, with its mingled web of life, we are each alone. Below the surface there is a deep, and below the deep there is a deeper depth. In the depth of the human heart there is, and there must be, solitude. There is a limit to the possible communion with another. We never completely open up our nature to even our nearest and dearest. In spite of ourselves something is kept back. Not that we are untrue in this, and hide our inner self, but simply that we are unable to reveal ourselves entirely. There is a bitterness of the heart which only the heart knoweth; there is a joy of the heart with which no stranger can intermeddle; there is a bound beyond which even a friend who is as our own soul becomes a stranger. There is a Holy of Holies, over the threshold of which no human feet can pass. It is safe from trespass, guarded from intrusion, and even we cannot give to another the magic key to open the door. In spite of all the complexity of our social life, and the endless connections we form with others, there is as the ultimate fact a great and almost weird solitude. We may fill up our hearts with human fellowship in all its grades, yet there remains to each a distinct and separated life. We speak vaguely of the mass of men, but the mass consists of units, each with his own life, a thing apart. The community of human life is being emphasized to-day, and it is a lesson which bears and needs repetition, the lesson of our common ties and common duties. But at the same time we dare not lose sight of the fact of the singleness of human life, if for no other reason than that, otherwise we have no moral appeal to make on behalf of those ties and duties. In the region of morals, in dealing with sin, we see how true this solitude is. There may be what we can truly call social and national sins, and men can sin together, but in its ultimate issue sin is individual. It is a disintegrating thing, separating a man from his fellows, and separating him from God. We are alone with our sin, like the Ancient Mariner with the bodies of his messmates around him, each cursing him with his eye. In the last issue, there is nothing in the universe but God and the single human soul. Men can share the sinning with us; no man can share the sin. "And the sin ye do by two and two, ye must pay for one by one." Therefore in this sphere of morals there must be limits to friendship, even with the friend who is as our own soul.