'Grass' is natural truth, and 'flower of the field' is spiritual truth, as in Isaiah 40:5, 6. Green grass, in the Word, signifies the good and truth of the church, and of faith, which first springs up in the natural man. This is also signified by 'herb in the field.' Grass and the pulse of the herb, as in Psalm 32:2, signify what is most vile. Grass signifies science from a spiritual origin, or that by which spiritual truth is confirmed. 'Reeds and rushes' signify science from a sensory origin, or the things which confirm the fallacies of the senses, as in Isaiah 25:7. This science, considered in itself, is only a part of the lowest natural degree, which may be justly called material and bodily, in which there is little or no life. Green grass also signifies that which is alive with man. 'Grass burnt up' signifies the things which are dead in him. Grass signifies the scientific principle. Just as green grass serves animals for support, spiritual truth serves men for spiritual nourishment.

(References: Apocalypse Explained 507)

664. Verse 11. And after the three days and a half, signifies when it is finished, thus the end of the old church and the beginning of the New Church. This is evident from the signification of "the three days and a half," as being fullness and completion as to the end of the old church, when there is the beginning of the New Church (See above, n. 658). It is said "after the three days and a half" because in the Word "days" signify states, here the last state of the church; for in the Word all times, as "hours," "days," "weeks," "months," "years," "ages," signify states, as here the last state of the church, when there is no longer any good of love or truth of faith left. Because "days" signify states, and the establishment of the Most Ancient Church is treated of in the first chapter of Genesis, and it becomes established successively from one state to another, it is there said:

That there was evening and there was morning the first day, the second, the third, the fourth, the fifth, and the sixth days, even to the seventh, when it was finished (Genesis 1:5, 8, 13, 19, 23, 31; 2:2);

and the "days" there do not mean days, but the successive states of the regeneration of men at that time, and the consequent establishment of the church with them. So also elsewhere in the Word.