In Matthew 15:3-9 and Mark 7:6-13, Christ strongly rebukes the Pharisees for failing to follow the law of God. He authoritatively quotes from two sections of the law: one from the Decalogue, and one outside the Decalogue. It was not simply the fifth commandment that Christ cites as binding, but even the penal sanction specifying capital punishment for incorrigible children is held forth by our Lord as an obligation. Christ made no artificial distinction between "moral" laws and their "civil" punishments. Whereas the Pharisees nullified God's law by their traditions, Christ upholds its integrity and validity in exhaustive detail. Whereas the Pharisees wold easily let a son be released form his obligation to support his parents, Christ endorses the severity and strictness of God's law. The antinomian traditions of men cannot be used to "break" Scripture apart. Christ does not explain away His citation of the prescription of capital punishment for incorrigible children; in fact, He gives absolutely no indication that He feels it needs any argument at all. .... [Greg L. Bahnsen, Theonomgy in Christian Ethics, p. 254]
And he said to them, “Well did Isaiah prophesy of you hypocrites, as it is written,And he said to them, “You have a fine way of rejecting the commandment of God in order to establish your tradition! For Moses said, ‘Honor your father and your mother’; and, ‘Whoever reviles father or mother must surely die.’ But you say, ‘If a man tells his father or his mother, “Whatever you would have gained from me is Corban”’ (that is, given to God)—then you no longer permit him to do anything for his father or mother, thus making void the word of God by your tradition that you have handed down. And many such things you do.” (Mk. 7:6-13)
“‘This people honors me with their lips,but their heart is far from me;
in vain do they worship me,
teaching as doctrines the commandments of men.’
You leave the commandment of God and hold to the tradition of men.”
We have said that Bahnsen needs to prove that God's law is a simple category. For most of the book, Bahnsen simple assumes that God's law is a simple category. He largely ignores the distinction between moral and civil law, and explains ceremonial law in such a way that it functions in some sense like the moral law (in its "restorative" function). But since the general Reformed tradition does recognize the distinction between the moral, civil and ceremonial law, Bahnsen cannot just assume that the law is a simple category, and claim that since the moral law is still valid, therefore all the law is still valid.
Here in page 254 is probably the major place where Bahnsen actually tries to deal with his denial of the legitimacy of the "civil law" concept, by subsuming everything into the "moral law." According to Bahnsen, Jesus cites Matthew 15:3-9 and Mark 7:6-13, which includes the penal sentence of death for incorrigible children, and he approves of it. Therefore there is no such thing as "civil law" per se, since all "civil law" is moral. Here however is where Bahnsen misreads the Gospel narratives. We must look at what Jesus is trying to drive at when he cites from the OT, not just assume that everything in the verses Jesus cites is binding today. The purpose of Jesus' citing those passage is to impress and contrast the differences the OT laws have concerning obedience to parents with the way the Pharisees have distorted the law. The gravity of the 5th commandment is that those who rebel against parents are to be put to death, while the Pharisees allowed for rebellion by spurious dedication to God. That is the contrast Jesus is trying to portray. In other words, the penal sanction of the 5th commandment is there to impress upon us the gravity of the sin as opposed to how flippantly the Pharisees treated it. It says nothing whatsoever whether Jesus approves of the penal sanctions of the 5th commandments. Elsewhere Bahnsen warns against arguing from silence, so likewise he should have kept to his principle here and not argue that Jesus approves of the penal sanctions of the 5th commandment.
The main problem with the theonomic denial of the category of "civil law" is it does not reckon with the eschatological focus of Jesus' coming. Jesus' first coming is His coming in grace; His second coming is a coming in judgment. Now is the time of pilgrimage of God's people, not the time of conquest. Just as Abraham lived among a foreign people with their rules, so likewise believers live among unbelievers with their rules. Therefore, while God's moral law is ubiquitous for all peoples everywhere, being written on their hearts (Rom. 2:15), God's civil law is meant for a time of conquest, not a time of pilgrimage. The civil code is meant when God is the ruler of the civil realm as well, and thus is not suited for the inter-advent period. When the Old Testament prophets called the other nations to account (e.g. Amos), it was to their violations of moral principles that these nations were condemned (Amos 1:3-2:3), not because for example they failed to execute their rebellious children, or the specific rejection of the Mosaic law (Amos 2:4) which they did not receive.
It is not "autonomy" to claim that life in this world is more grey than it is black and white. God's law remains true, and His moral law is still normative, and we are to promote that moral law in society since it is still applicable for all. But to promote the civil aspect of the law is to confuse Christ's rule at His second coming with Christ's rule now in grace. Does this mean that those who commit grievous moral sins like murder are exempt from the death penalty? Not necessary! What it does say is that one cannot argue for a one-to-one correlation between the civil law and how Christians ought to call the magistrate to enforce the moral law.
Bahnesen is in error in his interpretation of the episode in Matthew 15:3-9 and Mark 7:6-13. In line with that, Theonomy's denial of the category of "civil law" is therefore in error because it confuses the nature of Christ's kingdom now. Just because the magistrate is obligated to uphold God's moral law is does not mean that it is obligated to uphold the civil law as well, and that is the main practical error of Theonomy.