“And every wild animal of the earth and every bird in the heavens and every animal creeping on the earth, in which there is a living soul—every green plant will serve them for nourishment”; and so it was done. — Genesis 1:30
This verse depicts the spiritual person’s earthly food. The wild animal of the earth symbolizes such a person’s earthly plane of existence, as does the bird in the heavens, both of which received for nourishment the green plant or grass. Concerning this person’s two kinds of food—both earthly and spiritual—David has the following to say:
Jehovah causes grain to sprout for the beast and plants for the service of humankind, to bring bread from the earth. (Psalms 104:14)
“The beast” stands for the wild animal of the earth and at the same time for the bird in the heavens, both of which David mentions in verses 11 and 12 of the same Psalm.
In this verse the nourishment of the earthly self is restricted to green plants for the following reason.
While we are being reborn and learning to concern ourselves with the spirit, we are in constant battle (which is why the Lord’s church is described as militant). Up to this point our cravings have controlled us, because our whole being is cobbled together out of nothing but those cravings and the distorted ideas they spawn. We cannot rid ourselves of those longings and distortions instantaneously during regeneration; to do so would destroy us completely, since we have not yet acquired another way of life. Consequently, evil spirits are left with us for a long time to trigger our appetites, which then break down in countless different ways, and break down so thoroughly that the Lord can turn them into something good. This is the way we reform.
In the time of battle, evil spirits leave us no other nourishment than the equivalent of green plants. (Those spirits hold an absolute hatred for everything good and true—for anything having to do with love for the Lord and faith in him, these being the only good and true things that exist—because such things hold eternal life within them.) But from time to time the Lord gives us additional food that can be compared to seed-bearing plants and fruit trees: calm and peace, with their accompanying joy and happiness.
If the Lord were not protecting us every moment, every split second, we would be wiped out instantly. Hatred against any aspect of love for the Lord or faith in him dominates the world of spirits, and the hatred is so deadly that it defies description.
I can testify to the truth of this absolutely. For several years now I have visited the next world and the spirits there, though remaining in my body, and the evil ones (the worst, in fact) have crowded around me, sometimes numbering in the thousands. They have been allowed to spew out their venom and harass me in every possible way, but still they were unable to hurt a single hair on my head, so closely did the Lord guard me.
All these years of experience have taught me a great deal about the nature of the world of spirits and about the conflict that those who are being reborn inevitably suffer if they are to win the happiness of eternal life. No one, however, can learn enough from a general description to develop an unshakable belief in this information, so the details, with the Lord’s divine mercy, must come in what follows.
from Secrets of Heaven, Volune 1, Sections 58-59