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.

10229. 'And you shall take the silver of expiations from the children of Israel' means the purifying truths springing from good that are the Church's. This is clear from the meaning of 'the silver' as truth springing from good, dealt with in 1551, 2954, 5658, 6112, 6914, 6917, 8932; from the meaning of 'expiations' as purification from evils, dealt with above in 10218, so that 'the silver of expiations' is truth that purifies; and from the representation of 'the children of Israel' as the Church, dealt with in the places referred to in 9340. The words 'truth that purifies' are used because all purification from evils is effected by means of truths, see 2799, 5954, 7044, 7918, 9089. The implications of all this are that by himself a person thinks nothing but evil; for by himself he does not think about God nor about good and just behaviour towards his neighbour, unless it is to his own advantage. Nor indeed does he think about heaven and eternal life, only about the world and life there. As long as this is a person's state of mind his thought springs from what is below him and not from what is above him, thus from hell and not from heaven. To think what is good therefore a person's thought must spring from heaven, so that his mind must be raised in that direction. This is accomplished solely by means of truths such as exist within the Church, derived from the Word; for those truths teach about the nature of God, who the neighbour is, the existence of heaven, the reality of eternal life, and in particular what evil and good are. When these truths pass into the mind its inner levels are raised above the self, and are accordingly drawn away from those things below the self, thus away from evils. From this it may be recognized that all purification or removal from evils is effected by means of truths, which are therefore called purifying truths.