To understand what was really decided there, we need to look at and understand the historical, cultural and scriptural background.
From the beginning of gentile conversions, "certain men . . . from Judea" insisted that "unless you are circumcised according to the custom of Moses, you cannot be saved" (Acts 15:1 Acts 15:1And certain men which came down from Judaea taught the brothers, and said, Except you be circumcised after the manner of Moses, you cannot be saved.
American King James Version×). Notice that they viewed circumcision as a matter of salvation. It was a huge issue to them!
So Paul took the matter before Church leadership to be officially resolved (Acts 15:2 Acts 15:2When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas, and certain other of them, should go up to Jerusalem to the apostles and elders about this question.
American King James Version×). "But some of the sect of the Pharisees who believed rose up, saying, 'It is necessary to circumcise them, and to command them to keep the law of Moses'" (Acts 15:5 Acts 15:5But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.
American King James Version×). By the "law of Moses" they meant the imperatives of the Sinai Covenant, which would have included perhaps some of its rituals and ceremonies—and definitely circumcision.
At the Church conference in Jerusalem, both Peter and Paul addressed the assembled elders. The matter of circumcision, Peter noted, had already been settled by God Himself (Acts 15:7-9 Acts 15:7-9  And when there had been much disputing, Peter rose up, and said to them, Men and brothers, you know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe.
 And God, which knows the hearts, bore them witness, giving them the Holy Ghost, even as he did to us;
 And put no difference between us and them, purifying their hearts by faith.
American King James Version×). Peter's testimony gave proof that God gave the Holy Spirit to gentiles who were not circumcised (Acts 10:44-48 Acts 10:44-48  While Peter yet spoke these words, the Holy Ghost fell on all them which heard the word.  And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost.  For they heard them speak with tongues, and magnify God. Then answered Peter,  Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?  And he commanded them to be baptized in the name of the Lord. Then prayed they him to tarry certain days.
American King James Version×). As a result, they could only conclude that God does not require the circumcision of male gentile converts.
Paul and Barnabas then spoke, describing how God had performed miracles through them in calling gentiles into the Church (Acts 15:12 Acts 15:12Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles and wonders God had worked among the Gentiles by them.
American King James Version×).
Four restrictions on new gentile converts
James, the half-brother of Jesus Christ, then issued a concluding statement: "It is my judgment, therefore, that we should not make it difficult for the Gentiles who are turning to God. 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" (Acts 15:19-20 Acts 15:19-20  Why my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
 But that we write to them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood.
American King James Version×, NIV).
Some people seize on these words to argue that nothing more was required of early Christians—that they (and we) need not keep other laws found in the Old Testament.
But does this view really make sense? James said nothing about murder, stealing, lying, taking God's name in vain or a host of other sins. By this rationale, should we conclude that Christians are now free to do these evil things? Of course not! So why, then, did James list only these four restrictions—"to abstain from food polluted by idols, from sexual immorality, from the meat of strangled animals and from blood"?
The link connecting each of these requirements is idolatry. Specifically, each was directly associated with the pagan forms of worship common in the areas from which God was calling gentiles into the Church. Each also violated specific biblical commands (Exodus 20:2-6 Exodus 20:2-6  I am the LORD your God, which have brought you out of the land of Egypt, out of the house of bondage.
 You shall have no other gods before me.
 You shall not make to you any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth.
 You shall not bow down yourself to them, nor serve them: for I the LORD your God am a jealous God, visiting the iniquity of the fathers on the children to the third and fourth generation of them that hate me;
 And showing mercy to thousands of them that love me, and keep my commandments.
American King James Version×; Leviticus 20:10-20 Leviticus 20:10-20  And the man that commits adultery with another man's wife, even he that commits adultery with his neighbor's wife, the adulterer and the adulteress shall surely be put to death.  And the man that lies with his father's wife has uncovered his father's nakedness: both of them shall surely be put to death; their blood shall be on them.  And if a man lie with his daughter in law, both of them shall surely be put to death: they have worked confusion; their blood shall be on them.  If a man also lie with mankind, as he lies with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be on them.  And if a man take a wife and her mother, it is wickedness: they shall be burnt with fire, both he and they; that there be no wickedness among you.  And if a man lie with a beast, he shall surely be put to death: and you shall slay the beast.  And if a woman approach to any beast, and lie down thereto, you shall kill the woman, and the beast: they shall surely be put to death; their blood shall be on them.  And if a man shall take his sister, his father's daughter, or his mother's daughter, and see her nakedness, and she see his nakedness; it is a wicked thing; and they shall be cut off in the sight of their people: he has uncovered his sister's nakedness; he shall bear his iniquity.  And if a man shall lie with a woman having her sickness, and shall uncover her nakedness; he has discovered her fountain, and she has uncovered the fountain of her blood: and both of them shall be cut off from among their people.  And you shall not uncover the nakedness of your mother's sister, nor of your father's sister: for he uncovers his near kin: they shall bear their iniquity.  And if a man shall lie with his uncle's wife, he has uncovered his uncle's nakedness: they shall bear their sin; they shall die childless.
American King James Version×; Genesis 9:4 Genesis 9:4But flesh with the life thereof, which is the blood thereof, shall you not eat.
American King James Version×; Leviticus 7:26-27 Leviticus 7:26-27  Moreover you shall eat no manner of blood, whether it be of fowl or of beast, in any of your dwellings.  Whatever soul it be that eats any manner of blood, even that soul shall be cut off from his people.
American King James Version×).
It is evident, however, that the apostles also had another reason for singling out these links to idolatry. They wanted to make sure that new non-Jewish converts would have immediate access to learning the teachings of God's Word—the Holy Scriptures (Romans 15:4 Romans 15:4For whatever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope.
American King James Version×; 2 Timothy 3:15 2 Timothy 3:15And that from a child you have known the holy scriptures, which are able to make you wise to salvation through faith which is in Christ Jesus.
American King James Version×).
Notice the reason James expressed for listing those particular prohibitions: "For Moses has been preached in every city from the earliest times and is read in the synagogues on every Sabbath" (Acts 15:21 Acts 15:21For Moses of old time has in every city them that preach him, being read in the synagogues every sabbath day.
American King James Version×, NIV). The purpose for this somewhat puzzling concluding statement now becomes clear: The apostles wanted to ensure that every new gentile convert would be able to avail himself of that instruction as the words of Moses were "read . . . every Sabbath."
Access to the Scriptures
In that day no one had their own copies of the Bible. Scrolls were handwritten and enormously expensive. Only the very wealthy could afford any kind of personal library. The only places where one could hear the Bible regularly read was at the Jerusalem temple or in the Jewish synagogues that existed in larger cities of the Roman Empire.
By renouncing any associations with idolatry and choosing to worship only the true God of the Scriptures, these new gentile converts could attend the Jewish synagogue. There they would be able to learn the basic teachings of the Holy Scriptures every Sabbath. In areas where Christian congregations were not yet established, the synagogue was the only organized training center where the Scriptures could be learned.
Paul plainly confirms the importance of new converts being instructed from the Scriptures. In his letter to Timothy—a young minister who helped him serve these gentile converts—Paul makes the point that "all Scripture is given by inspiration of God, and is profitable . . . for instruction in righteousness" (2 Timothy 3:16 2 Timothy 3:16All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
American King James Version×).
He even reminded the gentile converts in Rome that "faith comes by hearing, and hearing by the word of God" (Romans 10:17 Romans 10:17So then faith comes by hearing, and hearing by the word of God.
American King James Version×). At that time, the only "Scripture" and "word of God" they knew was what we today call the Old Testament. The New Testament didn't yet exist.
Paul clearly expected his gentile converts to put effort into both hearing and learning the inspired Word of God. Yet when the Church first began accepting gentile converts, it did not yet have the capacity to instruct non-Jewish believers in the Scriptures in every city—especially in those cities having no Christian congregations.
But the Jews welcomed uncircumcised gentiles into the synagogue to learn God's truth—providing they made a commitment to serve only the true and living God of the Bible.
The New Testament shows that the earliest gentile converts quickly became familiar with those Scriptures. Because the Scriptures used by the Jews and Christians were exactly the same, the apostles were comfortable having new gentile believers join the Jews and Jewish Christians who attended synagogue services each Sabbath.
The Bible itself records that many gentiles first heard Paul's preaching in the synagogue where they were attending alongside the Jews (Acts 17:1-4 Acts 17:1-4  Now when they had passed through Amphipolis and Apollonia, they came to Thessalonica, where was a synagogue of the Jews:
 And Paul, as his manner was, went in to them, and three sabbath days reasoned with them out of the scriptures,
 Opening and alleging, that Christ must needs have suffered, and risen again from the dead; and that this Jesus, whom I preach to you, is Christ.
 And some of them believed, and consorted with Paul and Silas; and of the devout Greeks a great multitude, and of the chief women not a few.
American King James Version×; Acts 17:10-12 Acts 17:10-12  And the brothers immediately sent away Paul and Silas by night to Berea: who coming thither went into the synagogue of the Jews.  These were more noble than those in Thessalonica, in that they received the word with all readiness of mind, and searched the scriptures daily, whether those things were so.  Therefore many of them believed; also of honorable women which were Greeks, and of men, not a few.
American King James Version×; Acts 17:16-17 Acts 17:16-17  Now while Paul waited for them at Athens, his spirit was stirred in him, when he saw the city wholly given to idolatry.  Therefore disputed he in the synagogue with the Jews, and with the devout persons, and in the market daily with them that met with him.
American King James Version×). Both the synagogue and the Holy Scriptures were central to Paul's work in converting Jews and gentiles alike.
Both Paul and his converts regarded the Holy Scriptures—as taught by the Jews in the synagogues—as the foundation of their beliefs. Thus he did not always have to explain every detail of the way of life these new converts were to learn. When he was in a city for only a short time, Paul could concentrate his efforts on explaining the role and mission of Jesus Christ and then move on to another city.
He knew that gentile converts could continue receiving basic instruction in the Scriptures and God's way of life by attending the regular synagogue services. And the fact that, in his letters to gentile congregations, he quoted extensively from the same Scriptures used by the Jews provides clear evidence that all gentile converts had access to that instruction regardless of where they lived.