An earlier oath is seen in the thirteenth century grimoire Liber Juratus, where each person who came into possession of the book was not only tested for a year, but also obliged to swear:
“That it should be delivered to no woman, nor to any man except he were of lawful age, and he should also be both Godly and faithful, whose Godly behaviour had been tried for the space of a whole year, and that this book should no more hereafter be destroyed, but that it should be restored again to the honour, or to his successors, and if there cannot be found an able and a sufficient man to whom this book might be delivered, that then the master bind his executors by a strong oath to bury it with him in his grave.”
In the mystery cults of ancient Greece, the distinction was made between those who were initiates and the uninitiated, or magickal practitioners and non-practitioners. Likewise oaths of secrecy or a specific course of action sworn with dire consequences were common phenomena in the ancient world. The use of persuasive analogy in this manner is described in some detail by the modern Classics professor Fritz Graf in his study of magickal practices from the sixth century BCE through to late antiquity, Magic in the Ancient World, clearly demonstrating the practice of imprecation and consequence.
However, the concept of initiation itself is much older and examples of it, with components which are still found today in Wiccan initiation ceremonies, can be found throughout the ancient world. Such connections often occur in association with the mysteries of the deities which are still important in modern Witchcraft.
“The mysteries of the Cabiric worship were celebrated also at Thebes and especially at the Isle of Samothrace. They are said to have taken place at night. The candidate for initiation was crowned with a garland of olives, and wore a purple band round the loins. He was prepared by sacred ceremonies, probably hypnotic, and was seated on a brilliantly lighted throne, around which the other initiates danced in a mystic measure.” 
<1> The Religion of Babylonia & Assyria, Jastrow, 1893, also quoted in The Book of Witches, Hueffer, 1908
<2> An Historical Essay Concerning Witchcraft: With Observations Upon Matters of Fact, Hutchinson, 1718
Extract from: Wicca: Magical Beginnings written by d’Este & Rankine, 2008 (Avalonia.) PB / Kindle @ https://amzn.to/3Ay4HJr. Shared here with the intention to inspire and inform the now and future generations interested in Wicca and other Pagan traditions inspired by it.