It is, in short, too bad that Romulus should have had in Proculus an avoucher of his ascent to heaven, when the Christ of (this) god could not find any one to announce his descent from heaven; just as if the ascent of the one and the descent of the other were not effected on one and the same ladder of falsehood! Then, what had he to do with Galilee, if he did not belong to the Creator by whom that region was destined (for His Christ) when about to enter on His ministry? As Isaiah says: "Drink in this first, and be prompt, O region of Zabulon and land of Nephthalim, and ye others who (inhabit) the sea-coast, and that of Jordan, Galilee of the nations, ye people who sit in darkness, behold a great light; upon you, who inhabit (that) land, sitting in the shadow of death, the light hath arisen." It is, however, well that Marcion's god does claim to be the enlightener of the nations, that so he might have the better reason for coming down from heaven; only, if it must needs be, he should rather have made Pontus his place of descent than Galilee. But since both the place and the work of illumination according to the prophecy are compatible with Christ, we begin to discern that He is the subject of the prophecy, which shows that at the very outset of His ministry, He came not to destroy the law and the prophets, but rather to fulfil them; for Marcion has erased the passage as an interpolation. [Tertullian Adv Marc 4.7.3]This argument was developed by David Inglis. “But since both the place and the work of illumination according to the prophecy are compatible with Christ, we begin to discern that He is the subject of the prophecy, which shows that at the very outset of His ministry, He came not to destroy the law and the prophets, but rather to fulfil them; [c.f. Mt 5:17] for Marcion has erased the passage as an interpolation.”
Tertullian is referring to something in his copy of Lk that he did not see in Mcg, but what passage did he not see? At first sight he appears to be saying that the text we see in Mt 5:17 was in his copy of Lk, but not in Mcg. However, from the sentence construction it is more likely that he is just using Mt 5:17 to highlight the fact that, by his actions regarding “the place and the work of illumination according to the prophecy,” Christ in Mcg is fulfilling the same prophecies as Christ in Lk. As a result it is more likely that “the place and the work of illumination according to the prophecy” were not present in Mcg. The “work of illumination” is mentioned in Jesus’ reading in vv. 4:18-19:
The Spirit of the Lord is upon me, because he hath anointed me to preach the gospel to the poor; he hath sent me to heal the brokenhearted, to preach deliverance to the captives, [c.f. Isa 61:1a] and recovering of sight to the blind, to set at liberty them that are bruised, [c.f. Isa 61:1b] To preach the acceptable year of the Lord. [c.f. Isa 61:2a]
From this it appears that “and recovering of sight to the blind,” which is a reference to “the work of illumination” but is not part of Isa 61, was not in Mcg. The place of illumination is not referred to here, but is mentioned in Isa 9:1-2, previously quoted by Tertullian. Although we do not today see any reference to this passage in Lk, we do see a version of Isa 9:1-2 at Mt 4:14-16, at the beginning of the Capernaum passage:
And leaving Nazareth, he came and dwelt in Capernaum, which is upon the sea coast, in the borders of Zabulon and Nephthalim: [Mt 4:13] That it might be fulfilled which was spoken by Esaias the prophet, saying, [Mt 4:14] The land of Zabulon, and the land of Nephthalim, by the way of the sea, beyond Jordan, Galilee of the Gentiles; [Mt 4:15] The people which sat in darkness saw great light; and to them which sat in the region and shadow of death light is sprung up. [Mt 4:16]
It is possible that Tertullian saw this text in Lk, but it is instead more likely that in his copy v. 4:31 read the same as the variant in Bezae:
And came down to Capernaum, a city near the sea, in the borders ot Zabulon and Nephthalim, and taught them on the sabbaths.
The actual solution is that Marcion's text was the same as Clement's in Stromata 1. But that is an unnecessary diversion.