“Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished. (Mt. 5:17-18)
Μὴ νομίσητε ὅτι ἦλθον καταλῦσαι τὸν νόμον ἢ τοὺς προφήτας· οὐκ ἦλθον καταλῦσαι ἀλλὰ πληρῶσαι. ἀμὴν γὰρ λέγω ὑμῖν· ἕως ἂν παρέλθῃ ὁ οὐρανὸς καὶ ἡ γῆ, ἰῶτα ἓν ἢ μία κεραία οὐ μὴ παρέλθῃ ἀπὸ τοῦ νόμου, ἕως ἂν πάντα γένηται. (Mt. 5:17-18)
There is reason to hold that the phrase "law or prophets" is best taken as focusing on the ethical stipulations contained in the canon of the entire Older Testament. The context of Matthew 5:17 clearly demonstrates that both "the law" and "the prophets" refer to divine demand and not prophecy or promise. Verse 16 preceding deals with "good works"; indeed, throughout the entire sermon Jesus speaks as the Messiah who promulgates God's will (cf. Matt. 7:28ff). Verses 21-48 correct misinterpretations of the divine demands. Matthew 7:12 (cf. Matt. 22:40) uses "the law and prophets" exclusively of moral demands. And most telling is the fact that verses 18 and 19 following, which explain and apply verse 17 of Matthew 5, mention only the law. The entire passage is concerned primarily with Christ's doctrine, not His life. ... The concern of Matthew 5:17 is Christ's doctrine as it bears upon theonomy (God's law). While "law or prophets" broadly denotes the Older Testament Scriptures, Jesus' stress is upon the ethical contents, the commandments, of the Older Testament. [Greg L. Bahnsen, Theonomy in Christian Ethics (25th Anniversary Multimedia Edition; Nacogdoches, TX: Covenant Media Foundation, 2002), 53]
In his book, Bahnsen spent a significant section discussing the interpretation of Matthew 5:17-20. In it, Bahnsen tries to prove that Matthew 5:17-20 teach the "abiding nature of God's law in exhaustive detail." Note that there are four things Bahnsen has to prove: (1) "God's law" is a simple category, (2) a continuity of "God's law" from the Old to the New Testament, (3) total continuity (4) in "exhaustive detail." It is not sufficient to prove continuity, and then throw the Dispensational slur on those who disagree on what you think "continuity" is. Much of Bahnsen's arguments in his 500+ page work amount to proving what Covenant Theologians have always agreed upon: the establishment of one Covenant of Grace that spans both the Old and New Testaments, the continuity of God's moral law from the Old and the New, the gracious attitude of God in giving His law and covenant to Israel, the validity of the Decalogue as regulatory law for the Christian life, and that Jesus did not do away with the moral law in His earthly ministry. As such, we can easily interact with His work on the vital points where I would say he is in error.
Bahnsen claims that the context of Matthew 5, the Sermon on the Mount, is all about imperatives, commands, and ethics. Now that makes sense, but is that what it only is? Is the context only on ethics? I would suggest not!
It is widely noted that Jesus' Sermon on the Mount parallels Moses and the giving of the Ten Commandments on Mount Sinai. Jesus is portraying Himself as the new Moses as it were, proclaiming God's law to the people. In this sense, it is true that Jesus is the new Moses, the new lawgiver. But we note here the eschatological portrayal of this kingdom of which Jesus is proclaiming its law. It is a kingdom not of this world, as we can see in the Beatitudes. It is the law of Christ in the spiritual kingdom, whereby those who are persecuted and reviled are the inheritors of the Kingdom. This eschatological focus therefore should color our interpretation of Jesus as the new lawgiver, for surely it would be astonishing and impractical for policies of national defense to be founded on the policy of "turning the other cheek" (cf. Mt. 5:39)! Now, Bahnsen recognizes this and makes the distinction between private and public responses, which is true, but such only makes sense when it is not just seen as a mere private response but a response fitting to the new eschatological kingdom that Christ is inaugurating. One would not find this command of turning the other cheek in the Old Testament, which even allowed for personal vengeance on those who killed others, thus the need for cities of refuge and rulings concerning manslaughter (Num. 35:9-34). We note here that the avenger who kills outside the city of refuge the one who unintentionally killed another is exonerated of wrongdoing (Num. 35:26-7), even though the judge might have previously acquitted the killer as killing him unintentionally.
This eschatological flavor should help us interpret Matthew 5:17-20. The focus is indeed on imperatives in the Law and the Prophets, the two being one shorthand for the Old Testament (the Torah and the Neviim). But it is on imperatives as they are fulfilled in Christ's person and ministry, not mere ethics. It is on Christ fulfilling the imperatives through His active obedience. Bahnsen claims the context is that of Jesus as a teacher (p. 63), which is true, but the context is actually that of Jesus not just as a teacher, but as the eschatological teacher, AND Messiah, the fulfiller of righteousness and prophecy. Yes, it is not prophecy per se (p. 52), but rather imperatives fulfilled in Christ. This is the eschatological slant, and it is here that an examination of the Greek words help.
The word for "to fulfill" is the aorist infinitive πληρῶσαι, which is contrasted with the infinitive καταλῦσαι. Now certainly is is true that the two infinitives are set up as antonyms, and thus πληρῶσαι whatever its meaning must be the opposite of καταλῦσαι, which is "to destroy or make void." Bahnsen of course sees this and says that πληρῶσαι must mean "confirm," it being the antonym of "annul." But here we note that there is more than one antonym for "destroy/ annul / make void." If we read the text in its eschatological context, then the antonym for "annul" is merely "to fulfill," "to bring to completion/ fruition." Thus, Matthew 5:17 is Jesus saying that He is not making void the Old Testament with its laws and statues, but rather He is bringing them all to completion and fruition in Him, in His person and work, and only in this eschatological light is the imperatives relevant to us secondarily.
The closest Bahnsen deals with something analogous to this interpretation is his attempt to refute a sense of πληρῶσαι as "finish, or end" by stating that "it always appears in a context where the thought of advancement or moving on, as well as a temporal element, are explicit" (p. 57). Now that is not what we mean by "bringing to fruition," for we do admit that the imperatives do not just disappear because Christ fulfills them. Rather, we are saying that Christ "transmutates" them; all imperatives are now to be seen Christocentrically! There is a definitive shift form the Old to the New economy of things, while the substance do remain the same. Evidences of such a shift have already been mentioned earlier in the Beatitudes and the forgiving nature of the commands as it deal with issues like personal vengeance. Just because the substance remains the same from the Old to the New Covenants does not mean that there is absolute continuity between the two economies of salvation. In this light, it is illuminating here that Bahnsen, in reacting against the "New Torah" interpretation of the Sermon on the Mount, claims that such would be contrary to the principle of continuity between the Old and New economies (p. 49), evidently confusing continuity with absolute continuity, as if one equals the other.
In Greek of course, there is a word suitable for what Bahnsen wants to argue for: ἵστημι ("to establish/ appoint"). Bahnsen dismisses the word as being "simpler and less expressive" or "pithy" compares to the supposedly stronger word πληρόω (p. 74). While it is true that we should not critique the choice of Greek words as favoring one interpretation over another, it should give us pause as to the supposed explanation Bahnsen gave for why Matthew uses the word πληρόω instead of ἵστημι. It should also open the possibility to us that Matthew wanted to convey a meaning different from the word ἵστημι, and point us in the direction of eschatological fulfillment.
Moving on, Bahsen attempts to use the phrase "not one iota or dot" to argue for continuity in exhaustive detail (pp. 75-6). If one takes Bahnsen's view of the Sermon on the Mount being mainly ethical in nature, then of course that would seem to be the natural manner of interpreting the text. However, from the eschatological point of view, that only points out that Jesus will not fail to bring any of the imperatives to fruition through His person and work, and it does not speak anything about the nature of imperatives from the Old to the New Testament. In fact, Jesus' commands about divorce IS stricter than the Mosaic code (c.f Lev. 20:10, Deut. 24:1-4, Mt. 5:31-2), and thus we see that there is a shifting that has occurred. All of the imperatives are relevant for us, but only as seen in Christ.
In conclusion, we have seen that Bahnsen, and Theonomy, needs to prove four premises in order for theonomy to be a valid biblical position. Premise 2 is held as true by all, yet we have pointed out some problems with the type of continuity called for in Theonomy and thus call into question premise 3. From at least one example concerning divorce, we can question premise 4 as well, as the phrase "not one iota or dot" have to do with the law as they appear, not as to the law as applicable in Christ.