As Christians we can learn from the tanakh (5 books of Moses) and the prophets, psalms, all of scripture, as per 2 Timothy 3:16 All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness,
This "Scripture" being referred to is obviously the old testament, as the NT scriptures had not been compiled (nor written) yet as of Paul writing this letter to Timothy.
However we must be careful to not mix the covenants, you can get into quite a mess by trying to mix the new covenant with the covenant made at Sinai, and if you do mix the two, you have fallen from grace.
I am of the opinion it is great to obey any and all commandments, including the dietary laws, maybe even circumcision, but what you must not do, according to the New Testament is make these MANDATORY on the gentile Christians who are to walk in the Spirit.
Galatians 5:1-4
It is for freedom that Christ has set us free. Stand firm, then, and do not let yourselves be burdened again by a yoke of slavery.
2 Mark my words! I, Paul, tell you that if you let yourselves be circumcised, Christ will be of no value to you at all. 3 Again I declare to every man who lets himself be circumcised that he is obligated to obey the whole law. 4 You who are trying to be justified by the law have been alienated from Christ; you have fallen away from grace.
Remember that Paul also circumcised Timothy himself, so we aren't to take this verse and say, anyone who has gotten circumcised after becoming a Christian is lost, the issue is, there were certain pharisees who taught it was necessary to be circumcised in order to be saved, this was what Paul was fighting against. If you get circumcised with the idea that you will be justified in the eyes of God by it, you have fallen from grace. Proof of my claim that the issue was salvation, not just circumcision done for health, or cultural reasons:
Acts 15:1 Certain people came down from Judea to Antioch and were teaching the believers: “Unless you are circumcised, according to the custom taught by Moses, you cannot be saved.”
As to the dietary laws, even secular science shows that they were brilliant, pork is a very nasty meat full of parasites, garbage feeders like shrimp etc. .also spoil very easily. So, is it a bad thing to obey the dietary laws? Certainly not. Is it a bad thing to say a Christian is sinning by eating pork? Its more than bad, I'd say its a SIN! Jesus said:
Mark 7:18-19
“Are you so dull?” he asked. “Don’t you see that nothing that enters a person from the outside can defile them?
For it doesn’t go into their heart but into their stomach, and then out of the body.” (In saying this, Jesus declared all foods clean.)
Jesus declared all foods clean, however this does not mean that a Christian can just eat whatever he chooses, all meats are clean just like in the days of Noah, but certain foods are still to be avoided by Christians in the new covenant, proof:
Acts 15:20
Instead we should write to them, telling them to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood.
So even after the new covenant is in effect, you should not eat blood, or food sacrificed unto idols. The latter is also repeated by Jesus in the book of Revelation as he rebukes a church for doing this.
Me personally I come from a place where "Blood sausage" is a regular treat, and I have eaten it, now I no longer eat it. It is tasty, but we must go by what the New Covenant teaches us, not our own opinions.
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Sorry for a long rambling post, but one thing I would like to add about the all foods being clean and blood still being avoided, we are basically back to how things were BEFORE the law of Moses was given. This was the same rules Noah had from GOd, that we are under today:
Genesis 9:3-4 Every moving thing that lives shall be food for you. I have given you all things, even as the green herbs. But you shall not eat flesh with its life, that is, its blood
I tried to explain this to someone who believes we need to keep the food laws but ironically i was told i am "going all over the bible" to prove my point by quoting Genesis 9........ Meanwhile they quoted Leviticus to me.. Go figure!
TL;DR All laws are GOOD to obey, but its a SIN to demand obedience to circumcision, food laws, holydays, new moons, etc from other Christians in the new covenant.