It's necessary to consider the context in which the Council of Jerusalem made their declaration, as described in Acts 15.
And to do that one has to go back to events that happened more than 2600 years before that.
The Seven Laws.
Laws which were supposed by the Rabbis to have been binding upon mankind at large even before the revelation at Sinai, and which are still binding upon non-Jews.
The term Noachian indicates the universality of these ordinances, since the whole human race was supposed to be descended from the three sons of Noah, who alone survived the Flood.
— LAWS, NOACHIAN - JewishEncyclopedia.com
These laws, commonly known as the Noahide Laws, or Noachian Laws, are:
- not to worship idols.
- not to blaspheme the name of God.
- to establish courts of justice.
- not to kill.
- not to commit adultery.
- not to rob.
- not to eat flesh that had been cut from a living animal.
Judaism does not proselytize, and does not believe that Gentiles should obey God's commandments as delivered through Moses, but it does believe that these seven laws do apply to everyone, and views Gentiles that obey these Noahide laws as good people.
The only place that prospective converts to the early Christian Church could study the scriptures was in a Synagogue.
For Gentiles to be admitted and allowed to view the holy scrolls, they would have to be known to obey the Noahide Laws.
These Roman and Greek proselytes came from moral and law-abiding backgrounds (especially the ascetics, who saw anything pleasurable as sin), so they would already take for granted the concept of courts of justice and the laws against theft, murder, and blasphemy.
But within their society, they had commonly worshiped idols, used temple prostitutes, and eaten flesh from animals that still had life in them (i.e. contained blood).
Now, in that context, consider Acts 15:17–21:
17 So that the rest of mankind may seek the LORD,
Even all the Gentiles who are called by My name,
Says the LORD who does all these things." [Amos 9]
18 Known to God from eternity are all His works.
19 Therefore I judge that we should not trouble those from among the Gentiles who are turning to God,
20 But that we write to them to abstain from things polluted by idols, from sexual immorality, from things strangled, and from blood.
21 For Moses has had throughout many generations those who preach him in every city, being read in the synagogues every Sabbath.
- The restrictions correspond exactly to the Noahide Laws that the proselytes weren't already following.
- It mentions reading the holy scrolls in the synagogues.
- The ruling is directed at "the Gentiles who are turning to God", those that are still learning and have not yet converted to Christianity.
Many of Paul's epistles are directed at over-zealous Christians who are trying to subject proselytes and other interested people to the full Christian way of life.
For many of them, especially ascetics and dualists, this is too much and too soon, and Paul warns that this attitude is going to scare these people away from Christianity, not convert them.
For instance, people that have spent their whole life as vegetarians aren't suddenly going to start eating meat simply because they are considering becoming Christian.
Forcing them to eat animal flesh is an unreasonable burden to impose, and their personal feelings are going to take them a long time to change.
The Church cannot reasonably expect the proselytes to follow all of Gods laws yet; not until they are ready for their conversion.
(Even today, Judaism has a similar rule for proselytes.
In fact, not only are they not expected to follow all the rules, up until their conversion they are required to break some of them.
Proselytes for example must violate the Sabbath each week.)
Acts 15:28 and 29 tells us that basically all of the old law covenant is no longer to be observed except:
It says that proselytes and other interested people should not be forced to obey the biblical commandments, ceremonies, rituals, etc.
It does not say they aren't allowed to follow the laws when they are ready to do so, and it certainly doesn't say anything about converted Christians (who are expected to follow God's laws).
Believing that these are the only laws Christians must obey makes little sense.
Otherwise murder, theft, etc. would be considered acceptable behaviour.
except: … these necessary things
The Noahide Laws are "necessary", because that's the minimum requirement that the proselytes will have to do to be accepted by the Jewish community in order to have access to the holy scriptures and engage in discussion about them.
Are Christians under obligation to avoid any or all of those 4 things today?
Of course they are.
The Noahide Laws apply to all mankind, not only to Christians or Jews.
I would like an overview of mainstream Christian groups' interpretation of this scripture
Most mainstream Christian groups (i.e. the Roman Church and the various Protestant denominations that branched from it) have generally abandoned these (and many other) biblical laws.
They treat Acts 15 either as something specific for the time and place, or as associating blood with sacrifices to idols, and either way it is irrelevant today.
The Roman Catholic Church sees this prohibition as symbolic, doesn't feel obliged to enforce it, and uses syncretism to promote ecumenism:
From the viewpoint of exegesis the explicit reason for this prohibition is not exactly theological, it rather reflects a symbolical representation: “the life (nepheš) of all flesh is in the blood” (Lev 17.11, 14; Deut 12.23).
After the apostolic era the Church did not feel obliged to make this a basis for formulating precise rules for the butcher and the kitchen, and still less in our own times to prohibit blood transfusion.
The trans-cultural value underlying the particular decision of the Church in Acts 15 was a desire to foster the harmonious integration of the various groups, albeit at the price of a provisional compromise.
— The Bible and Morality - Biblical Roots of Christian Conduct, Pontifical Biblical Commission, 11 March 2008
Unlike Rome, the Eastern Orthodox Church however does prohibit the consumption of blood:
Actually – and this is not well-known – the Orthodox position is that the Apostolic Council is still binding, and this includes the prohibition on eating blood.
Two canonical sources which uphold the restriction of Acts 15 are:
Canon LXIII (63) of the Apostles: If any bishop, or presbyter or deacon or anyone else on the sacerdotal list at all, eat meat in the blood of its soul, or that has been killed by a wild beast, or that has died a natural death, let him be deposed.
For the Law has forbidden this.
But if any layman do the same let him be excommunicated.
Canon LXVII (67) from the Quinesext Council: Divine Scripture has commanded us to ‘abstain from blood, and strangled flesh and fornication’ (Gen 9:3-4, Lev 17 & 18:3, Acts 15: 28-29).
We therefore suitably penance those who on account of their dainty stomach eat the blood of any animal after they have rendered it eatable by some art.
If therefore anyone from now on should attempt to eat the blood of any animal in any way whatsoever, if he be a clergyman, let him be deposed from office; but if he be a layman let him be excommunicated.
The great Orthodox canonists (Zonaras, Balsamon) have reaffirmed the applicability of these canons.
— Eating Food that has Blood in It according to Canon Law
The Orthodox Church seems to be the only mainstream denomination that abstains from blood.
Although individuals may personally find the thought of consuming blood distasteful, there is no other mainstream Christian doctrine about this topic, either requiring or forbidding it.
Within the rest of mainstream Christianity consuming blood (or biblical unclean animals) is now an irrelevant secular issue, no different from that of eating broccoli or sauerkraut.
Many other denominations that didn't originate from the Roman Church also abstain from blood, but they aren't considered "mainstream".
Like mainstream Christianity, Seventh Day Adventists believe that the prohibition against eating blood was only temporary.
But unlike most denominations, rather than eventually allowing blood they believe the exact opposite: their long-term position is that meat of any kind should not be eaten:
It was not until after the Flood that meat in any form was permitted.
This was an emergency measure, and given only because vegetation was destroyed during the Flood, and it would take a period of time for it to be restored.
Certain definite restrictions were placed on its use then. It was not to contain blood.
"These necessary things" (Acts 15:19, 20, 28, 29) include abstinence from blood as commanded when meat was first allowed after the Flood.
Thus, we see that man has never been given permission to eat meat as it is ordinarily eaten today.
— Ministry Magazine | Nutrition According to the Bible
Jehovah's Witnesses believe that the dietary laws were strictly part of the covenant with Israel, but they also recognize that eating or drinking blood is forbidden to all mankind.
Their belief that life is in the blood is so strong, that this includes not consuming blood by any means, such as receiving blood products during medical surgery:
This is a religious issue rather than a medical one. Both the Old and New Testaments clearly command us to abstain from blood. (Genesis 9:4; Leviticus 17:10; Deuteronomy 12:23; Acts 15:28, 29) Also, God views blood as representing life. (Leviticus 17:14) So we avoid taking blood not only in obedience to God but also out of respect for him as the Giver of life.
— Why Don’t Jehovah’s Witnesses Accept Blood Transfusions?.
Like Jehovah's Witnesses, Rastafarians also do not believe in the medical use of blood, nor does their diet include meat from unclean animals.
Their version of "kosher" is known as Ital, (the word "Vital" without the "V").
Like Seventh Day Adventists, they too aim for vegetarianism.
"Church of God"ists follow the biblical dietary laws.
(E.g. What Does the Bible Teach About Clean and Unclean Meats? | United Church of God.), but allow the medical use of blood:
Sometimes it’s been interpreted that the biblical law against eating blood means that people also shouldn’t have blood transfusions.
Since there’s no dogmatic statement on a modern medical procedure like a blood transfusion in the Bible, it’s up to the individual to make decisions about health care and treatment programs.
— What Does the Bible Say About Getting Blood Transfusions? | United Church of God
in light of the vastly different conditions we have now with most of us never being involved in the slaughter of the animals we consume
Some societies do deliberately eat or drink blood (e.g. German blood sausages), but generally most animals today are slaughtered in ways that allow the animal to bleed to death, draining the circulatory system of blood.
The red "blood" that one sees running out of raw meat isn't blood (haemoglobin), it is myoglobin, which performs a similar function but remains within the muscles and doesn't circulate.
In terms of modern meat production, there is only a small difference between common slaughter and Kosher/Halal slaughter.
The ritual slaughter uses an extremely sharp knife (painless) to cut through the throat without touching the spinal cord.
This results in almost immediate loss of consciousness while allowing the heart to continue pumping the blood out through the severed arteries.
(A prayer is also recited during the process.)
Common slaughter first stuns the animal with a blow to the head before the throat is cut.
To allow proper bleeding, this stun must be light enough that it doesn't actually kill the animal, so the force used is set to err on the side of being too little rather than too much.
Strangely, most animal-rights advocates mistakenly believe that the ritual killing is more cruel.
What must adherents of denomination X do or not do to demonstrate they are abstaining from blood?
Demonstrating that one is doing the right thing was big with the Pharisees (e.g. ritual hand washing before and after meals), but really has no part in Christianity (or Judaism).
God knows what everyone is doing and why they are doing it; what other people think is irrelevant.