From Arcana Coelestia ~ Emanuel Swedenborg
Every man has an internal and an external; his internal is called the internal man, and his external the external man; but what the internal man is, and what the external, is known to few. The internal man is the same as the spiritual man, and the external is the same as the natural man; the spiritual man is that which understands and is wise from those things which are of the light of heaven, but the natural man from those things which are of the light of the world (concerning which two lights see AC 3138). For in heaven there are nothing but spiritual things, whereas in the world there are nothing but natural things. Man has been so created that in him spiritual things and natural things, that is, his spiritual and natural man, should agree or make a one; but in this case the spiritual man ought to dispose all things in the natural, and the natural ought to obey, as a servant his lord.But by the fall the natural man began to exalt itself above the spiritual man, and thus inverted Divine order itself; hence the natural man separated itself from the spiritual, and no longer possessed any spiritual things, except such as could enter as through chinks, and confer the capacity of thinking and speaking. But in order that spiritual things might again flow into the natural man, this had to be regenerated by the Lord; that is, truth out of the natural man must be initiated and conjoined with good in the rational; and when this is effected, spiritual things come to the natural man, for then the light of heaven flows in and enlightens the things in the natural man, and causes them to receive light; the goods therein the heat of light, that is, love and charity; and the truth the rays of light, that is, faith; and in this way natural good and natural truth receive spiritual things. In this case natural good is all the delight and pleasure that come from having as an end the being of service to what is spiritual, thus to the neighbor, still more to the public weal, and still more to the Lord's kingdom, and above all to the Lord; and natural truth is all the doctrine and memory-knowledge that has as an end to be wise, that is, the doing of these things.
(AC 3167)