What Theosophy Is (Chapter I, page 4)

In its capacity as a religion, too, Theosophy gives its followers a rule of
life, based not on alleged commands delivered at some remote period of the
past, but on plain common sense as indicated by observed facts. The
attitude of the student of Theosophy towards the rules which it prescribes
resembles rather that which we adopt to hygienic regulations than obedience
to religious commandments. We may say, if we wish, that this thing or that
is in accordance with the divine Will, for the divine Will is expressed in
what we know as the laws of Nature. Because that Will wisely ordereth all
things, to infringe its laws means to disturb the smooth working of the
scheme, to hold back for a moment that fragment or tiny part of evolution,
and consequently to bring discomfort upon ourselves and others. It is for
that reason that the wise man avoids infringing them--not to escape the
imaginary wrath of some offended deity.

But if from a certain point of view we may think of Theosophy as a
religion, we must note two great points of difference between it and what
is ordinarily called religion in the West. First, it neither demands belief
from its followers, nor does it even speak of belief in the sense in which
that word is usually employed. The student of occult science either _knows_
a thing or suspends his judgment about it; there is no place in his scheme
for blind faith. Naturally, beginners in the study cannot yet –know- for
themselves, so they are asked to read the results of the various
observations and to deal with them as probable hypotheses--provisionally to
accept and act upon them, until such time as they can prove them for
themselves.

Secondly, Theosophy never endeavours to convert any man from whatever
religion he already holds. On the contrary, it explains his religion to
him, and enables him to see in it deeper meanings than he has ever known
before. It teaches him to understand it and live it better than he did, and
in many cases it gives back to him, on a higher and more intelligent level,
the faith in it which he had previously all but lost.

Theosophy has its aspects as a science also; it is in very truth a science
of life, a science of the soul. It applies to everything the scientific
method of oft-repeated, painstaking observation, and then tabulates the
results and makes deductions from them. In this way it has investigated the
various planes of Nature, the conditions of man's consciousness during life
and after what is commonly called death. It cannot be too often repeated
that its statements on all these matters are not vague guesses or tenets of
faith, but are based upon direct and oft-repeated –observation-- of what
happens. Its investigators have dealt also to a certain extent with
subjects more in the range of ordinary science, as may be seen by those who
read the book on Occult Chemistry.

A Textbook of Theosophy by C.W. Leadbeater (1912).