Marcion accepted only St. Luke’s Gospel, and mutilated that (Tertullian, Adv. Marcion. iv. 2).  He thus got rid of the testimony of the Apostles and eye-witnesses, Matthew and John, and represented the Law and the Gospel as contradictory revelations of two different Gods.  For this Cyril calls him ‘a second inventor of mischief,’ Simon Magus (§ 14) being the first.