"The chief difficulty which prevents men of science from believing in divine as well as in nature Spirits is their materialism"

The quote by H. P. Blavatsky is describing the trouble that scientists have in believing in divine and nature spirits due to their materialistic views. Materialism is the belief that just physical matter exists which all phenomena can be explained by physical laws. This view is in direct opposition to the belief in divine and nature spirits, which are spiritual entities that can not be explained by physical laws. Researchers, who are trained to believe in regards to physical laws, find it difficult to accept the existence of spiritual entities. This difficulty is what avoids them from believing in divine and nature spirits. Blavatsky's quote is a tip that science and spirituality are not mutually unique, and that it is possible to accept both.