Both Clement’s language in his letter to Theodore and the text of secret Mark that he cites suggest some kind of ritual. Secret Mark’s reference to waiting six days, coming at night, being naked under a linen cloth, and being taught “the mystery of the Kingdom of God” all suggests a ritual initiation. Clement’s language also suggests a ritual including statement that secret Mark “would, as a mystagogue, lead the hearers into the innermost sanctuary of that truth hidden by seven veils.” A mystagogue was a person who oversaw Greek mystery rites, a point I’ll discuss in a later post. Clement’s declaration that secret Mark is “most carefully guarded” in Alexandria “being read only to those who are being initiated into the great mysteries,” is a pretty explicit reference to ritual language. Clement’s statement about how Mark “did not divulge the things not to be uttered, nor did he write down the hierophantic teaching of the Lord” also has ritual language: a hierophant was like a mystagogue.
Morton Smith, who found the document and wrote the first book about it, argued that secret Mark suggested that Jesus “developed his spiritual gift into a technique by which he was able to ascend to the heavens and also to give others the same experience and similar spiritual powers.” Smith argued that Jesus began with John’s baptism “since it removed sin and presumably also impurity … and thus made the initiate fit to enter the heavens” and then added elements that can be “guess[ed] from Paul.” Smith notes Phil 2.5-11 and 1 Tim 3.16 to argue for a rite of ascent to the heavens based on I and II Enoch. “Such parallels,” argues Smith, “establish a strong presumption that Paul got these ideas from Jesus’ Palestinian followers, who got them from Jesus himself.” Smith suggests that Jesus initiated some of his disciples into this rite and even argued that Christ did so at Gethsemane based on Mark’s reference to the young man under the linen cloth (Mark 14:49-50).
Smith speculates that Jesus initiated a handful of disciples, “But even if some of the early disciples succeeded in repeating Jesus’ rite of possession and ascension, their initiations of a few individuals, one by one, were soon overshadowed,” by group spiritual experiences in the church. “Consequently, the developments which Jesus had added to the Baptist’s baptism fell into disuse or were preserved as ‘great mysteries’ for most advanced candidates.”
This idea of a secret ritual was suggested by a number of fathers, particularly Clement of Alexandria. Catholics had long claimed that many elements of the liturgy were part of the disciplia aracani (secret practices not mentioned in the scriptures) and Jean Danielou had argued that Clement’s secret tradition included a rite of ascent to heaven.
Smith’s book was controversial not only because of secret Mark but also because Smith continually referred to the secret ritual as “magical.” Smith compounded the controversy with his later highly controversial work Jesus Magician. Furthermore, many took secret Mark to be implying that some homosexual act was going on (because of the naked youth, I guess). Smith did not make this interpretation in Clement of Alexandria and a Secret Gospel of Mark (1973) but may have later (I haven’t read Jesus Magician). Either way, opponents of secret Mark throw around the charge that it suggests that Jesus was a gay magician. As I’ve argued a lot around here, “magic” is a very problematic category that scholars should not use. If one overlooks some of Smith’s terminology, it’s quite an interesting book.
While a number of other scholars do argue that Clement’s letter and secret Mark do suggest a rite, while some others who accept the letters validity try to argue against a ritual. Scott Brown explicitly argued against a rite in his book Mark’s Other Gospel: Rethinking Morton Smith’s Controversial Discovery, saying it was simply a higher teaching. But Brown’s later attempt to describe the nature of the teaching sort of makes it sound like a ritual. Highlights include, “When we examine what the imagery of entering the innermost sanctuary denotes in Clement’s writings we realize that this ‘space’ was inaccessible to catechumens and ordinary believers; like the great mysteries that it contains, this sanctuary was accessible only to the Christian equivalent of the Jewish high priest, which Clement called the true gnostic.” “The whole process constitutes an ascent.” “Clement’s cosmology owes a great deal to Philo’s allegorical interpretation of the wilderness tabernacle as a symbolic embodiment of the universe.” “Beyond this veil lies the Ogdoad (‘eight’), the inner sanctuary or ‘holy of holies’ of the celestial temple.” “Clement’s imagery of unveiling the holy of holies therefore implies a series of veils that divide the innermost sanctuary into a series of chambers…. Presumably, the chambers correspond to distinct regions within the Ogdoad.” “A comparable mystical tabernacle theology occurs in the Dead Sea Scrolls, especially the Songs of the Sabbath Sacrifice, which envisions the adept ascending through a series of seven temples/heavens in his approach to the divine throne.” “The idea that the experience of entering the holy of holies is the prerogative of the gnostic is hard to miss in Clement’s various discussions.”
In my following posts, I’ll discuss in more detail possible contexts for the possible ritual, particularly the Judeo-Christian apocalypses.
 Morton Smith, Clement of Alexandria and a Secret Gospel of Mark (Cambridge: Harvard University Press, 1973), 244, 243, 245, 254.
 Jean Danielou, “Les Traditions secretes des Apotres,” Eranos Jahrbook 31 (1962).
 See the Wikipedia entry. See notes 26 and 34.
 Scott G. Brown, Mark’s Other Gospel: Rethinking Morton Smith’s Controversial Discovery (Waterloo, Canada: Wilfrid Laurier University Press, 2005), 130, 141-42.
 Scott G. Brown, “Behind the Seven Veils, I: The Gnostic Life Setting of the Mystic Gospel of Mark” in Ancient Gospel or Modern Forgery?: The Secret Gospel of Mark in Debate, ed. Tony Burke (Eugene, Oregon: Wipf and Stock, 2013), 249, 253, 256, 263, 269, 273, 277. For Clement, the gnostic was a spiritually advanced Christian, different from the heretical groups that scholars apply the term to today.