XV.  Then comes the Sacred Night, the Anniversary of the confused darkness of the present life, into which the primæval darkness is dissolved, and all things come into life and rank and form, and that which was chaos is reduced to order.  Then we flee from Egypt, that is from sullen persecuting sin; and from Pharaoh the unseen tyrant, and the bitter taskmasters, changing our quarters to the world above; and are delivered from the clay and the brickmaking, and from the husks and dangers of this fleshly condition, which for most men is only not overpowered by mere husklike calculations.  Then the Lamb is slain, and act and word are sealed with the Precious Blood; that is, habit and action, the sideposts of our doors; I mean, of course, of the movements of mind and opinion, which are rightly opened and closed by contemplation, since there is a limit even to thoughts.  Then the last and gravest plague upon the persecutors, truly worthy of the night; and Egypt mourns the first-born of her own reasonings and actions which are also called in the Scripture the Seed of the Chaldeans Judith v. 6. removed, and the children of Babylon dashed against the rocks and destroyed; Ps. cxxxviii. 9. and the whole air is full of the cry and clamour of the Egyptians; and then the Destroyer of them shall withdraw from us in reverence of the Unction.  Then the removal of leaven; that is, of the old and sour wickedness, not of that which is quickening and makes bread; for seven days, a number which is of all the most mystical, We are to part with leaven for seven days (Exod. xii. 15), that is, with sin for the whole week of this life.  The number Seven Days signifies the passing of time which revolves in weeks.  And this number is mystical, because it is virgin and signifies virginity and the angelic life; for it alone, as arithmeticians teach, of all the numbers within the decade, is neither a multiple nor a measure, and also contains in itself the Four and the Three.  For there are four elements of the world, and the Trinity is their Creator.  He calls it co-ordinate with the world, because the world was made in seven days, and again because when seven thousand years are completed the end of the world is to come (Nicetas).  S. Augustine (Civ. Dei. c. ii. 31) says that the number Seven often stands for the Universe, because it is made up of Four which is altogether even (2 and 2 the sum of two even numbers) and Three which is altogether uneven (1 and 1 and 1). and is co-ordinate with this present world, that we may not lay in provision of any Egyptian dough, or relic of Pharisaic or ungodly teaching.