The high regard for their master is shown in the description of Marcion as the 'chief' of the bishops (Megethius in Adamantius I.8; was this common?), further still in the establishment of a Marcionite era (Tertullian I.19) and finally in the teaching that in heaven Paul sits at Christ's right hand and Marcion at the left (Origen Homilly XXV in Luk. T. V. 181. The idea is reflected in the three line inscription at Lebaba: in the first line one reads Marcion's name, in the middle line that of Jesus Christ, and in the third the name of Paul, though the latter as the name of a Marcionite presbyter). But at least at first Marcion was not awarded the name of 'apostle,' his congregation; biblicism forbade that. It is Tertullian who writes (IV 9. ANF III. 355): "Christ ... intending one day to appoint the shipmaster Marcion his apostle ..." But Tertullian himself knows nothing of Marcion's own people regarding him as an apostle. Otherwise he could not have written in De carne Christi 2 (ANF III, 522): "Show me your authority. If you are a prophet, foretell us a thing; if you are an apostle, open your message in public." Finally, it is only a polemical fencing stroke when Ephraem writes (Hymn 56): "Among the Marcionites it is not said, 'Thus says the Lord' but 'Thus says Marcion.'" Nevertheless the Marcionite church could not look at it any other way than that their founder belonged in the history of salvation in the broader sense of the term; for Christendom, after its second fall, which it committed by misunderstanding and backsliding from Paul (the first fall came between Christ and Paul), would have fallen back into the worship of the Creator God had not Marcion put it back on the right track. Marcion would continue to play the role in the church, at least, that some dogmaticians of the seventeenth century ascribed to Luther, when they devoted a special article to him, 'De vocatione Lutheri.' In addition, one later witness, Maruta, reports - certainly exaggerating - " Instead of Peter they set Marcion as head of the apostles." [von Harnack Marcion note 18 p. 166]
It has long been noted that von Harnack developed Marcion into a precursor to Luther and thus most of his reconstruction of the life of the 'heretic' can quickly be dismissed. Nevertheless von Harnack is the best witness to all the sources. One can easily turn this same evidence around and argue that from the earliest witness - Tertullian - there are testimonies of 'Marcion the apostle' (Irenaeus has nothing to say at all about Marcion the man). Eznik also declares that Marcion received the 'unspeakable' revelation of 2 Cor 12.4.
I also find the statement in Tertullian " if you are an apostle, open your message in public" cited above very interesting because it suggests a secret doctrine and - as we have already noted elsewhere - a secret gospel. It is worth noting that von Harnack finds evidence of a 'secret doctrine' or mystery religion at the heart of Marcionitism from the testimony of the Fihrist.
Marcion is still very much like St. Mark in the Alexandrian tradition. Not only is he the head of the Church, but he sits in a throne, his successors are the representative of Christ on earth, there is a rivalry with Peter and most importantly the rest of the world outside of Egypt denies that St. Mark is 'really' an apostle or that his successors represent the 'true' heads of the Church.
I will be posting the whole of R Casey's article on the Marcionite Diatessaron tomorrow ...
