No study of mysticism can be complete without a mention of Gnosticism. Gnosticism is the mother of modern, so called, Mystery Schools or Mystery Religions . While all of them may not be direct descendants, they are at least stepchildren, receiving nourishment from the many philosophies spun-off from Gnosticism.
First century Christians understood that the life of the church depended upon the existence of apostles.  This dependence is due to the keys that the apostles held.  Among the keys, that if lost, would signal the end of the church, were the keys to the mysteries or ordinances. Even a modern day bishop, who has some keys, can only rightly exercise those keys under the eventual direction of an apostle (an apostle holds all the keys).
Before leaving the first century church, Jesus gave Peter the authority to bind the mysteries or ordinances on earth, which shall be binding in heaven:
“And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.” (Matt. 16:19)
When the Prophet Joseph was given those same keys in this dispensation, the associated instructions tied the keys to the mysteries:
“And I have given unto him the keys of the mystery of those things which have been sealed , even things which were from the foundation of the world” (D&C 35:18)
When the apostasy of the original church began, and there were no longer apostle available, there was no one to correct the doctrines of men, and administer the mysteries.
The mysteries are the center of the church. The true church is built upon the mysteries. When the first original church fell:
“… a horde of deceivers ‘who up until then had been lurking in dark corners,’ as soon as they saw that there were no more apostles left to call them to account, came boldly forth, each claiming that he alone had the gnosis which the Lord had secretly imparted to the apostles after the resurrection.” 
The reason for this claim of the gnosis, hidden knowledge, or ordinances; is because the authorized (keys) holder of the true gnosis is the prophet of God on earth, and the leader of God’s church. 
The false prophets lured membership by a claim that they had the gnosis. To convince onlookers a whole arsenal of tricks were employed. They put on airs with pomp and circumstance, wearing robes, fancy hats, ringing the bells, making smoke, and burning incense. All of which were hollow gestures because they had no authority and only a corrupted version of ordinances.
These would be usurpers divided into groups, and come down to us today as the Mystery Schools .
Since the beginning of the apostasy, even until today they have fed off of each other by integrating each other’s claims into their own philosophy. They have become a hybrid of hidden and occult practice, a great “esoteric sponge.”
Gnostics, Rosicrucians, Theosophist and others initiate their members into what fragments of the gnosis they can find, mingled with the philosophies of men, and the doctrines of devils.
The watered down versions of these Gnostic views are the modern esoteric and New Age movements.
The well-grounded, mature saint can study Gnosticism and find truth, and all truth is beneficial. But, a steady diet of Gnosticism, without a daily good portion of a gospel meal, tends to sicken the soul.
 Ephesians 2:20
 Matthew 16:19, Revelation 1:18, Doctrine and Covenants 13:1, 27:6, 9, 12, 13, 42:69, 65:2, 81:2, 90:2 and so on.
 Hugh Nibley, Todd M. Compton, Stephen D. Ricks, Mormonism and Early Christianity, Deseret Book, Chapter 5.
 Apostles are prophets, seers, and revelators. Each one holds all the keys necessary to maintain the church on earth. If there is more than one apostle on earth, the senior (by setting apart date) is the leader of the church.