What Theosophy Is (Chapter I, page 2)

It deals with the present by describing what man really is, as seen by
means of developed faculties. It is customary to speak of man as having a
soul. Theosophy, as the result of direct investigation, reverses that
dictum, and states that man-is-a soul, and -has-a body--in fact several
bodies, which are his vehicles and instruments in various worlds. These
worlds are not separate in space; they are simultaneously present with us,
here and now, and can be examined; they are the divisions of the material
side of Nature--different degrees of density in the aggregation of matter,
as will presently be explained in detail. Man has an existence in several
of these, but is normally conscious only of the lowest, though sometimes in
dreams and trances he has glimpses of some of the others. What is called
death is the laying aside of the vehicle belonging to this lowest world,
but the soul or real man in a higher world is no more changed or affected
by this than the physical man is changed or affected when he removes his
overcoat. All this is a matter, not of speculation, but of observation and
experiment.

Theosophy has much to tell us of the past history of man--of how in the
course of evolution he has come to be what he now is. This also is a matter
of observation, because of the fact that there exists an indelible record
of all that has taken place--a sort of memory of Nature--by examining which
the scenes of earlier evolution may be made to pass before the eyes of the
investigator as though they were happening at this moment. By thus studying
the past we learn that man is divine in origin and that he has a long
evolution behind him--a double evolution, that of the life or soul within,
and that of the outer form. We learn, too, that the life of man as a soul
is of, what to us seems, enormous length, and that what we have been in the
habit of calling his life is in reality only one day of his real existence.
He has already lived through many such days, and has many more of them yet
before him; and if we wish to understand the real life and its object, we
must consider it in relation not only to this one day of it, which begins
with birth and ends with death, but also to the days which have gone before
and those which are yet to come.

Of those that are yet to come there is also much to be said, and on this
subject, too, a great deal of definite information is available. Such
information is obtainable, first, from men who have already passed much
further along the road of evolution than we, and have consequently direct
experience of it; and, secondly, from inferences drawn from the obvious
direction of the steps which we see to have been previously taken. The goal
of this particular cycle is in sight, though still far above us but it
would seem that, even when that has been attained, an infinity of progress
still lies before everyone who is willing to undertake it.

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