PLEASE HELP ME :((What is the main idea of this paragraph?

Although the old division of chemistry into inorganic and organic is still kept up as a
matter of convenience, the old boundaries between the two have been eliminated.
The distinction arose from the fact that there used to be (and are still to a very great
extent) a number of highly complex substances the composition of which is known,
for they can be analyzed, or taken to pieces, but which the wit of man has failed to put
together. Consequently, these substances could only be obtained from organic
bodles. The living trees, or animals, could in some mysterious way bring these
combinations about but man could not. The molecules of these substances are much
more complicated than those with which the inorganic chemist deals. The important
Ingredient in them all is carbon. In addition, hydrogen, nitrogen and oxygen almost
completes the list of the simple elements of which these marvelous substances are
compounded. In some cases, there appear to be hundreds of atoms in the molecule.