This psychological phenomenon was brought about mainly by the efforts of two men... Thomas Henry Huxley and Ernst Heinrich Haeckel. Both were fervent… - Gottfried de Purucker

The cause of the disappearance of the Mysteries has always been degeneracy, faithlessness on the part of the students, and their lack of an imperative and heart-reaching call for light. Where there is a genuine spiritual and intellectual call issuing from both heart and mind, there invariably comes the response by way of a new installment of teaching from the Brotherhood. (Chapter 22)

It was pointed out that a messenger or envoy is sent from the Brotherhood into the world for the purpose of striking anew a keynote of spiritual truth when a sincere call comes from the heart of mankind; but it must likewise be stated that, just as Krishna points out in the Bhagavad-Gita (4:7-8), an avatara comes in times of great spiritual barrenness, when the waves of materialism are rising high. (Chapter 22)

Even as the Christ-child, in the beautiful Christian legend, is said to have been born on December 25th, so likewise was the Mithraic divinity said to have been born into human form on that same day of the year, which was the winter solstice. This day, or one a few days thereafter, has been commemorated as the birthday of other religious type-figures also. (Chapter 2)