These are rules for the bhikkhus, and not for the lay people, of course.
The reason for prohibiting damaging plants is described in a sutta, but I forget the sutta’s name. It is described how a bhikkhu cut down a tree to make a hut for himself or something like that. There are bhummatta devas (devas of the lowest deva realm that reside alongside us), and most have their residences (vimana) on trees.
– Of course, we cannot see them or their residences, so we don’t know which tress are “taken” by such devas. Anyway, this bhikkhu cut down that tree and the deva got upset and complained to the Buddha. That is when the Buddha made this vinaya rule for the bhikkus.
– Furthermore, there are numerous insects and microscopic living beings that are sustained by a tree. There could be many insects on a single leaf! All those will be harmed by cutting down a tree.
Seeds and raw meat: There are microscopic living beings living in seeds. We all have seen even larger insects in various kinds of grains. The same apply to raw meat too. If bhikkhus start cooking such items, those lives would be destroyed.
Basically, the idea is that a bhikkhu is supposed to be taken care by the lay disciples. Thus, there is no need to cut down trees or to cook grains and raw meat (or engage in many activities stated in that sutta).
A lay person would not be able to abide those two rules, since he/she may have to cut down trees for many purposes and need to cook grains and meat.
The main idea is to avoid as many actions as possible, that could harm living beings. But there are some things that even a bhikkhu cannot avoid. For example, we know that there are numerous microscopic beings in water, and when we heat water or even drink water, they will die. But there is no way to live without water!
I recommend this sutta to everyone. The English translation Akvan referred to is good enough, since it does not involve any deep concepts and only the moral standards for a bhikkhu. We, as lay people, can try to live by most of those rules too, except some like the two Akvan mentioned.
P.S. There is more information on this topic at, “Tuvaṭaka Sutta – 4.14. The Quick Way“.
