37. As for the statement that 'the lights will be for signs, and for set times, and for days, and for years', this contains more arcana than can be presented at this point, though no arcanum at all is visible in the sense of the letter. For now only this can be said: Change in spiritual and celestial things takes place both on general and on particular scales, and is comparable to changes that take place through the day and through the year. Changes through the day are from morning to midday, from then on to evening, and through the night to the morning. Changes in the year similar, from spring to summer, from then on to autumn, and through winter to spring. These bring changes in temperature and amount of daylight, and so in the fertility of the earth. Compared to such changes are the changes that take place in spiritual and celestial things. Life without changes and variations would lead to sameness, and so no life at all. Good and truth would not be recognized and identified, let alone perceived. In the Prophets such changes are called 'ordinances', as in Jeremiah,

[Thus] said Jehovah who gives the sun for light by day and the ordinances of the moon and of the stars for light by night, These ordinances will not depart from before Me. Jeremiah 31:35-36.

And in the same prophet,

Thus said Jehovah, If I have not established My covenant of day and night, the ordinances of heaven and earth . . . Jeremiah 33:25.

But these things will in the Lord's Divine mercy be dealt with at Genesis 8:12.

3167. 'And to [her] mother' means to natural truth also, that is to say, spiritual things passed from the rational to it, even as they passed to natural good, dealt with just above. This is clear from the meaning of 'a mother' as the Church, which by virtue of truth is called 'a mother', dealt with in 289, 2717. So that people may know how spiritual things pass to natural good and to natural truth as a result of truth being introduced into good in the rational, a brief description must be given here. Everyone has an internal and an external, his internal being called the internal man, and his external the external man. But few know what the internal man is and what the external. The internal man is one and the same as the spiritual man, and the external man one and the same as the natural man. The spiritual man depends for understanding and wisdom on things that belong to the light of heaven, whereas the natural depends for its understanding and wisdom on things that belong to the light of the world. Regarding those two kinds of light, see 3138. For in heaven none but spiritual things exist, whereas in the world none but natural exist. The human being was created in such a way that in him spiritual things and natural things, that is, his spiritual man and his natural man, should accord with each other or make one. But in that case the spiritual man ought to have control over the things in the natural, and the natural man ought to obey, like a servant his master.

[2] Through the Fall however the natural man started to raise itself above the spiritual man and so turn Divine order itself upside down. As a consequence the natural man separated itself from the spiritual, and spiritual things could not reach it any longer except so to speak through chinks to provide the ability to think and speak. But so that spiritual things might flow in once more into the natural man this had to be regenerated by the Lord, that is, truth from the natural man had to be introduced and joined to good in the rational. When this happens spiritual things have access to the natural man, for now the light of heaven flows in and illuminates things in the natural man, and causes what is there to receive light. The goods there receive the warmth that the light conveys, which is love and charity, whereas the truth receives rays of light, which is faith. It is in this way that spiritual things pass from the rational into natural good and truth. Natural good in that case consists in all the delight and satisfaction gained from having service to the spiritual man as the end in view, and so service to the neighbour, more so to one's country, more so still to the Lord's kingdom, and above all to the Lord. And natural truth consists in all doctrinal teaching and factual knowledge which have wisdom, that is, the performance of those things, as the end in view.