On the subject of the law, Matthew and Luke are the most conservative books in the New testament. Matthew for obvious reasons, and you would think Luke too. But aside from Jacob Jervell (“The Law in Luke-Acts”, Luke and the People of God, pp 133-151), Philip Esler (Community and Gospel in Luke-Acts), and biblioblogger Richard Anderson, I haven’t run across many who are keen on the idea of Luke-Acts catering to Jewish sensibilities. Esler seems to have it right: the Lukan community was made up of Jews and Gentile God-fearers who had been painfully excluded from the synagogue. The Matthean community, meanwhile, consisted exclusively of Jews, in tension with the synagogue but not separate from it (Saldarini, Allison, etc). Matthew wanted to re-Judaize Christianity as much as possible, while Luke wanted to legitimate its development out of Judaism as much as possible. The law was esteemed by each in a different way.
In Matthew’s case, the Torah was to be followed in the context of messianic renewal (Mt 5:1-7:28), which called for internalization and intensification at the same time: thus were Jesus’ “new” teachings and Moses’ “old” equally valid (Mt 9:17 vs. Mk 2:22). He toughened teachings on the Levitical food laws (Mt 15:1-20 vs. Mk 7:1-23), cited Peter (who treacherously triumphed over Paul at Antioch for insisting on circumcision as the prerequisite for mixed table-fellowship) as the supreme authority (Mt 16:18), and like Peter before him had no use for mixed table fellowship (Mt 15:21-28 vs. Mk 7:24-30). He acknowledged that salvation had come to the Gentile nations (Mt 28:19) at the expense of Israel (Mt 21:43), but insisted that Jews keep a fair distance from foreigners despite this — or even because of it. Matthew was concerned with saving the lost sheep of Israel more than ever now (Mt 10:6), and re-Judaizing Christianity was the only way he saw this feasible.
Luke kept a conservative outlook on the law in general (Lk. 2:22-24, 39; Acts 21:17-26; 28:17), portraying Jesus as customarily attending synagogue (Lk 4:16), rewriting Mark (and even Matthew’s rewrite of Mark) in deference to the law (Lk 10:25-28 vs. Mk 12:28-34/Mt 22:34-40), and denying any ransom or atoning function of Christ’s death on the cross (Lk 22:27 vs. Mk 10:45/Mt 20:28; Lk 22:15-19a (19b-20 later additions) vs. Mk 14:22-25/Mt 26:26-29). His strategy was to show that Jesus respected the law for Jews as much as he transcended it for Gentiles. There was nothing radically “new” about Christianity (Lk 4:36 vs. Mk 1:27), and indeed the “old” was still desirable (Lk 5:39 vs. Mk 2:22). He was thus able to present Judaism as a legitimate faith which carried within itself the seeds of its own transformation — a transformation (supposedly) sanctioned by the most Judaic of Christians, Peter and James.
So Peter supposedly pioneered the mission to the Gentiles (Acts 10:1-11:18) instead of Paul (Gal 2:1-10). James supposedly agreed publicly with Paul that Gentiles needn’t be circumcised to share table-fellowship with Jews (Acts 15:19), and the two settled on a compromise set forth in the “apostolic decree” (Acts 15:20), instead of a private agreement about circumcision-free Gentiles by which James imposed no additional conditions (Gal 2:6). Christians with Pharisaical links supposedly caused the trouble at Antioch (Acts 15:1,5), instead of Peter and James (Gal 2:11-14) who treacherously broke the agreement reached earlier (Gal 2:1-10). And the split between Paul and Barnabus owed to disagreement over John Mark (Acts 13:13; 15:36-40) rather than Barnabus siding with Peter at Antioch (Gal 2:13). (see Esler, p 107)
That Luke felt compelled to claim the support of Peter and James by reversing their historical roles says a lot about his opposition. Peter and James were evidently being invoked by other Christians (like Matthew) as authorities against certain practices. Of course, Peter and James were historically more like Matthew, but that didn’t stop Luke from claiming them anyway — anymore than it stopped him from claiming the entirety of Judaic heritage:
“It was for his community of Jews and Gentile God-fearers, painfully excluded from the synagogue to which they had once belonged or which they had at least attended, that Luke fixed upon a legitimatory strategy which has often, both before and since, been adopted by the defenders of a new social order. He presented their new faith as if it were old and established, as the divinely sanctioned outgrowth of Judaism… So Luke could console his fellow-Christians with the message that it was not they but Jews still attending the synagogue who had abandoned the God of Abraham, Isaac, and Jacob, of Moses and of David.” (Esler, pp 69-70)
This means that Luke was sharply sectarian, while Matthew was not. Esler notes that Lk 4:28-30 is a key to understanding Luke’s sitz im leben (pp 56-57), since it is the only occasion in the synoptics where the Jews try to kill Jesus, apart from general plotting which leads to his crucifixion. (The only parallels are in the highly sectarian fourth gospel: Jn 5:18, 8:59, 10:31.) The passage indicates extreme animosity between Luke’s community and the synagogue. Matthew is another story. Texts like Mt 23:1-39 & Mt 27:25 (the woes against the Pharisees and the curse on the Jewish community), point to internal critique (which is often nasty) rather than external polemic: the Matthean community was deviantly competitive, but neither apostate nor sectarian.
But this raises the big question: what was so offensive about Luke’s community unlike Matthew’s? The answer turns on concrete practices rather than abstract beliefs. Christian belief in a crucified messiah, while deviant and misguided, would not have resulted in exclusion from the synagogue — or at least, not in an age where Jewish groups were floating different ideas about messiahship left and right. That’s precisely why the Matthean Christians could stay attached to it.
No, the actual practice which put Lukans beyond the pale is the same as that which distinguished Pauline and Markan Christianity: mixed table-fellowship between Jew and Gentile, which (as we’ve seen) Luke goes out of his way to portray Peter and James as condoning — even pioneering — when in fact they ultimately sided with Jewish tradition. The practice was offensive in the extreme, and was probably what hard-liners (like the pre-Christian Paul) persecuted Christians for. The Mattheans, following the authority of Peter (Mt 16:18; Gal 2:11-14), refused to engage in this practice.
We know this from the way Matthew revises his Markan source in Mt 15:21-28/Mk 7:24-30. While the Markan woman legitimates mixed table-fellowship by saying that even the dogs under the table eat from the children’s scraps, Matthew’s revision has her speaking of dogs eating scraps falling from the master’s table — meaning that the children (Jews) and dogs (Gentiles) no longer eat the same bread. (So Esler, p 92). (I would suspect that the diaspora communities addressed in James’ epistle avoided mixed table-fellowship just as the Mattheans did: Richard Bauckham makes a compelling case that James himself wrote the letter.) The dogs are now saved apart from the chosen who remain a light to the nations in their own way.
Matthew and Luke are instructive examples of “conservative Christianity” in different ways. Both were addressed to Jewish communities, though Luke’s included Gentile God-fearers. The Matthean Christians adhered to the Torah, though in the context of a messianic renewal, and were able to retain ties to the synagogue because of it. The Lukan Christians respected the Torah (far more than Paul and Mark) — the God-fearers as much as the Jews — but allowed for its transcendence in certain ways which ultimately alienated them from wider Judaism.