Theosophy recognizes seven kingdoms, because it regards man as separate from the animal kingdom and it takes into account several stages of evolution which are unseen by the physical eye, and gives to them the mediaeval name of "elemental kingdoms".
The divine Life pours itself into matter from above, and its whole course may be thought of in two stages--the gradual assumption of grosser and grosser matter, and then the gradual casting off again of the vehicles which have been assumed.

The earliest level upon which its vehicles can be scientifically observed is the mental--the fifth counting from the finer to the grosser, the first on which there are separated globes.

In practical study it is found convenient to divide this mental world into two parts, which we call the higher and the lower according to the degree of density of their matter.

The higher consists of the three finer subdivisions of mental matter; the lower part of the other four.
When the outpouring reaches the higher mental world it draws together the ethereal elements there, combines them into what at that level correspond to substances and of these substances builds forms which it inhabits.

We call this the first elemental kingdom.
After a long period of evolution through different forms at that level, the wave of life, which is all the time pressing steadily downwards, learns to identify itself so fully with those forms that, instead of occupying them and withdrawing from them periodically, it is able to hold them permanently and make them part of itself, so that now from that level it can proceed to the temporary occupation of forms at a still lower level.