Ephrem Used the Word 'Truth' in Association with the Episcopal Throne in the Exact Manner I Suggest Clement Did in To Theodore

From Lange's summary in The Portrayal of Christ in the Syriac Commentary on the Diatessaron:

Because Christ leaves the Church on earth after his ascension he promises to send the Spirit to the Apostles [XXI.33]. The Spirit becomes the pledge of life [ibid], revealer of truth [XIX.14]. She guides the Church so that it can remain the seat of truth [XI V.1 2]. Because of the Spirit's guidance, the Church becomes the perfect body of Christ [XIV.12]. Because of the Spirit's guidance the Church becomes the perfect body of Christ [XIV.24]

I will get the original material for which she is providing a summary shortly but the point again is that when Clement says that St. Mark "knew the interpretation would, as a mystagogue, lead the hearers into the innermost sanctuary of that truth hidden by seven veils" - he is saying that the Alexandrian autograph of the Gospel of St. Mark identifies its Episcopal 'throne of St. Mark' as being referenced in the Evangelist's original narrative.

If you are interested in reading how this observation fits within my greater understanding of the workings of Secret Mark WITHIN the contemporary Alexandrian Church please go here

If you want to read more about how Alexandrian Christianity was rooted in the Jewish traditions of Alexandria, Philo of Alexandria and more feel free to purchase my new book here