“Enq: This refers to the common origin of religions, and you may be right there. But how does it apply to practical brotherhood on the physical plane?
Theo: First, because that which is true on the metaphysical plane must be also true on the physical. Secondly, because there is no more fertile source of hatred and strife than religious differences.
When one party or another thinks himself the sole possessor of absolute truth, it becomes only natural that he should think his neighbor absolutely in the clutches of Error or the Devil.
But once get a man to see that none of them has the whole truth, but that they are mutually complementary, that the complete truth can be found only in the combined views of all, after that which is false in each of them has been sifted out – then true brotherhood in religion will be established. The same applies in the physical world.
Enq: Please explain further.
Theo: Take an instance. A plant consists of a root, a stem, and many shoots and leaves. As humanity, as a whole, is the stem which grows from the spiritual root, so is the stem the unity of the plant. Hurt the stem and it is obvious that every shoot and leaf will suffer.
So it is with mankind.
Enq: Yes, but if you injure a leaf or a shoot, you do not injure the whole plant.
Theo: And therefore you think that by injuring one man you do not injure humanity? But how do you know? Are you aware that even materialistic science teaches that an injury, however slight, to a plant will affect the whole course of its future growth and development? Therefore, you are mistaken, and the analogy is perfect.
If, however, you overlook the fact that a cut in the finger may often make the whole body suffer, and react on the whole nervous system, I must all the more remind you that there may well be other spiritual laws, operating on plants and animals as well as on mankind, although, as you do not recognize their action on plants and animals, you may deny their existence.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 