Selective use of Old Testament law
The Biblical Old Testament contains many laws that are not followed by Christians. Jesus defied various Old Testament laws such as performing work on the Sabbath (Luke 13:14 ) and not being concerned with "unclean" food laws (Mark 7:1-5, 14-19 ). However, Matthew 5:17 states:
- "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."
The specific laws that should be retained or abolished needs to be established by Christians. The reclassification of laws avoids some absurd Old Testiment laws being relevant and avoids these being used in counter-apologetics against Christianity. The selection of Old Testament law is justified by:
- Covenant Theology, Old Testament law applies unless it is abolished in the New Testament.
- Dispensational Theology, Old Testament law does not apply unless it is reiterated in the New Testament. This generally views the Old Testament law to have been given to a specific people at a specific time and does not automatically apply to Christians.
However, it is arguable that some Christians are cherry picking since some Old Testament laws are retained without a principled basis.
Examples of absurd or questionable Old Testament law
- "You shall not wear a garment of different sorts, such as wool and linen mixed together. (Deuteronomy 22:11 )"
- "And all that have not fins and scales in the seas, and in the rivers, of all that move in the waters, and of any living thing which is in the waters, they shall be an abomination unto you: They shall be even an abomination unto you; ye shall not eat of their flesh, but ye shall have their carcases in abomination. (Leviticus 11:10-11 )"
- "If two men are fighting and the wife of one of them comes to rescue her husband from his assailant, and she reaches out and seizes him by his private parts, you shall cut off her hand. Show her no pity. (Deuteronomy 25:11-12 )"
The Old Testament contains questionable sections on:
- Stoning unruly children
- Prohibition of Homosexuality
- The requirement of animal sacrifice.
The following is also mandated:
- Various activities that may not be done on the Sabbath, being Friday sunset to Saturday sunset.
Also, graven images are prohibited.
The New Testament condones the following, so these types of laws are arguably still in effect:
- Prohibition of Homosexuality 
- Slavery  is not observed by most Christians.
- Passover  is not observed by most Christians.
- Since the Ten Commandments were individually reiterated in the New Testament, most Christians consider all ten, or possibly nine,  were retained by Jesus.
- Observance of the Sabbath, being Friday sunset to Saturday sunset. This is not observed by mainstream Christianity but is observed by seventh-day Sabbatarians.
Ignored good stuff
There are occasional good teachings in the Old Testament.  Some of these teachings are routinely ignored by believers.
- Anti-xenophobia Leviticus 19:34
- Be kind to your enemies and strangers Exodus 23:4-5 Exodus 23:9 Psalms 38:7
- Love people, do not hate, do not oppress others Leviticus 19:17 Leviticus 25:17
- Help the poor Deuteronomy 15:7-8 Psalms 41:1
- Love peace not war Psalms 120:6-7
- Seek knowledge Proverbs 2:2 Proverbs 3:13-18
- Be merciful Proverbs 3:3
- Be kind to animals Proverbs 12:10
The select use of Old Testament laws is flawed in several respects. Believers quote other Old Testament laws and ignore ones they do wish to follow. There is no principled rule followed and theological reasoning is ignored when inconvenient.
New Testament counter evidence
- "Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven."
Jesus quoted an Old Testament law in light that it is still of God that Christians wouldn't normally follow,
- "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,’ (Mark 7:9-10 )."
Finally, decapitate their argument by quoting Jesus with:
- "Do not think that I have come to abolish the law or the prophets. I have come not to abolish but to fulfill. Amen, I say to you, until heaven and earth pass away, not the smallest part or the smallest part of a letter will pass from the law, until all things have taken place. (Matthew 5:17 )"
The New Testament still retains violent and capricious God
An illustration of this Trinitarian point: 
- "We are told explicitly that Jesus Christ IS THE GOD OF THE OLD TESTAMENT! You probably already accept this. But, by logical extension, you must also accept therefore that it was Jesus Christ who ordered the Israelites to slaughter millions of defenseless men, women and children in the conquest of Canaan; it was Jesus Christ who killed every firstborn child in Egypt; it was Jesus Christ who ordered king Saul to butcher thousands of children and babies in the genocide of the Amalakites; it was Jesus Christ who ordered the Israelites to capture and mass-rape 32,000 young girls of the Midianite tribe after killing their families; it was Jesus Christ who struck dead 50,000 innocent people at Beshemish for merely looking into the ark of the covenant; it was Jesus Christ who caused the painful asphyxiation of every man, woman, child and animal on the face of the earth during the flood of Noah (with the exception of 8); and it was Jesus Christ who condemned every person ever born to a state of eternal suffering, all because 6000 years ago a curious and naive woman ate a piece of fruit."
The New Testament, despite being much smaller and covering a much shorter period of time in its story, nonetheless manages room for some "Old Jealous God"-style condemnations. Gospel of Matthew, 10:11-15 :
- "Whatever town or village you enter, search for some worthy person there and stay at his house until you leave. As you enter the home, give it your greeting. If the home is deserving, let your peace rest on it; if it is not, let your peace return to you. If anyone will not welcome you or listen to your words, shake the dust off your feet when you leave that home or town. I tell you the truth, it will be more bearable for Sodom and Gomorrah on the day of judgment than for that town."
Are the people of said town merely to feel so ashamed that their experience is worse than burning alive? Or is this a literal threat against entire communities of people? Plenty of modern Christians — though not the true kind, of course — are perfectly okay with the latter interpretation, and, following from both Scripture and the doctrine of omnipotence, see the hand of God in plenty of natural disasters, as just punishment for said towns having at least one unbeliever.
Regarding Hell, Christopher Hitchens makes the following point:
- "The god of Moses would brusquely call for other tribes, including his favorite one, to suffer massacre and plague and even extirpation, but when the grave closed over his victims he was essentially finished with them unless he remembered to curse their succeeding progeny. Not until the advent of the Prince of Peace do we hear of the ghastly idea of further punishing and torturing the dead."
Jesus only has to mention the doctrine of Me-or-Hell once to automatically condemn billions more than the Old Testament ever does. And Jesus references Hell a lot.
In every major mainstream branch of Christianity, Jesus is considered to fully possess the nature of God. The largely-extinct Christian branch of Gnosticism treats as two separate deities. If a Christian wishes to contrast the "jealous Old God" with the "merciful New God", he is committing the Gnostic heresy by semantics, and should be very glad he does not live in a time and place where this could be punished with torture and/or death.
Do Acts and the epistles take precedence over the Gospels?
- Main Article: Differences between the Gospels and the epistles
The justification for ignoring Old Testament laws is often based on Acts and the epistles. The practices of the early church describe behaviours that seem at odds with the gospels. It perhaps illustrates the humans are very quick to re-interpret laws that are inconvenient. It is unclear why the gospels don't bother to mention details later "revealed" in Acts and the epistles. (The gospels were written the epistles after but set before.) Some of the "innovations" in Acts and the epistles:
- Ignoring circumcision (Acts 10 vs. Acts 15 ) and the Sabbath.
- Worship on the first day of the week (Sunday).
- Faith not works. Or Faith and works. Or possible faith or works (an idea later adopted by Pelagianism)
"smallest part or the smallest part of a letter" (also translated "jot or tittle"), is metaphoric hyperbole. Given that it is discussing the literal word-for-word structure of Old Testament texts, this makes one wonder how in the world poor Jesus can ever make his words taken seriously. Even when he says "Be a literalist about the Law", he's taken non-literally.
"All things", in fact, "have taken place". The world has, metaphorically, already ended with the crucifixion of Jesus, and we are in a new age. This view is called Preterism. It is not the mainstream view regarding Jesus's (and/or other Biblical speakers') discussion of the End Times.
It doesn't matter, because portions of the New Testament do explicitly overrule old laws, most especially kashrut dietary laws and certain rigid interpretations of keeping the Sabbath holy. Arguing that one's holy book contradicts itself, of course, doesn't exactly help one's case much. And despite those parts, nothing in the New Testament explicitly nullifies the old laws as a whole; there is nothing to suggest, for example, that the forbidding of wearing mixed clothing is no longer in effect. (Or that God is sorry for butchering all those people.)
- Do Christians have to obey the Old Testament law?
- Why Don’t Christians Follow All the Old Testament Laws?
- Abrogation of Old Covenant laws, Wikipedia