'A raven,' as in Genesis 8:7, signifies falsities. The spiritual self only knows general truths from the Word, and forms its conscience from these, and the general truths of the Word are accommodated to the fallacies of the senses. So countless falsities attach themselves, and insinuate themselves into those general truths, and they cannot be drawn out. These falsities are what 'the raven which went forth in going and returning' signifies. 'Sons of the raven,' as in Psalm 147:8, 9, signify natural people in a dim light arising from fallacies relating to divine truth.

(Odkazy: Arcana Coelestia 865)

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.