6. the Diatessaron heralded the coming of a 'Comforter' like Muhammad

those Semites who accepted the single, long gospel necessarily associated it with a political solution to their oppression - the appearance of the Christ heralded by Jesus.  Marcion was in a long line of people who used the single long gospel and whose 'Paraclete' reference heralded the coming of an individual rather than 'the Holy Spirit)

If Muhammad (or one of his informants or collaborators, in theory) had been familiar with the integrated Gospel, the Diatessaron, it is clear that, as far as he knew, the Diatessaron had probably been composed in Syriac. Having said that, it is not easy to know which Gospel text Muhammad could have been familiar with. However, there are a few rare direct references in the Qurʾān to the Gospels. Thus Q. 48: 29: “Such is their likeness in the Torah and their likeness in the Gospel— like as sown corn that sendeth forth its shoot and strengthenth it and riseth firm upon its stalk, delighting the sowers – that He may enrage the disbelievers with (the sight of) them. God hath promised, unto such of them as believe and do good works, forgiveness and immense reward." This text combines two Gospel pericopes – Mark 4:26–7 and Matthew 12:23 – the same amalgam that the Diatessaron makes, seen for example in the Middle-Dutch translation thereof, done in the thirteenth century from a lost Latin translation, and in the Arabic translations thereof. Van Reeth applies the same treatment to the passages of the Qur'an which pertain to the infancy of Mary (Q 3:35–48), John (Q 19:3), and Jesus (Q 3:37; 19:22–6), showing again that “le Coran témoigne de la tradition du Diatessaron.”108 He does the same again with the Docetist version of the Crucifixion of Jesus (Q 4:157), but in this case he refers to Angel-Christology (cf. G. Lüling), notably that of the Elkesaites, declaring: “Plutôt qu'un simulacre que Dieu aurait façonné et substitué au Christ pour être crucifié à sa place, il s'agit originalement de la forme humaine que Dieu a instaurée pour Jésus au moment de l'incarnation et dans laquelle sa personne transcendante et angélique pouvait descendre.”109 Even if the Diatessaron does not explain all of the Qur'anic particularities on the life of Jesus, Van Reeth makes the following conclusion: “En se référant au Diatessaron comme l'avait fait Mani avant lui, le Prophète Muhammad pouvait souligner l'unicité du message évangélique. En outre, il s'inscrivait dansla longue lignée de Marcion de Tatien et de Mani. Tous ont voulu (ré)tablir le vrai Évangile, afin d'en atteindre le sens original. Ils se croyaient autorisés à faire de travail d'harmonisation textuelle parce qu'ils s'assimilaient au Paraclet que Jésus avait annoncé.” [Claude Gilliot, The Authorship of the Quran in the Quran in its Historical Context p. 99]

The association with the single, long gospel with the expectation for a political ruler who was opposed to Caesar, a second century Muhammad if you will, helps explain why the text was repressed by the Roman Church undoubtedly with the 'assistance' of the Roman government (cf. Irenaeus Adv Haer 4.30.1 - 4).  When Irenaeus speaks of the heretics who 'divide Jesus and Christ' or 'two Christs' Jesus and the Jewish messiah, the expectation is related to a 'tradition' messianic figure being heralded by Jesus i.e. God descended from heaven to proclaim the advent of another.