15:4 When they had come to Jerusalem, 
they were received by the assembly and the apostles and the elders,
and they reported all things that God had done with them. 
15:5 But some of the sect of the Pharisees who believed rose up, saying, 
"It is necessary to circumcise them, and to charge them to keep the law of Moses." 
15:6 The apostles and the elders were gathered together to see about this matter. 
15:7 When there had been much discussion, Peter rose up and said to them, 

"Brothers, you know that a good while ago God made choice among you,
that by my mouth the Gentiles should hear the word of the gospel, and believe. 
15:8 God, who knows the heart, testified about them, 
giving them the Holy Spirit, just like he did to us. 
15:9 He made no distinction between us and them, cleansing their hearts by faith. 
15:10 Now therefore why do you tempt God, 
that you should put a yoke on the neck of the disciples
which neither our fathers nor we were able to bear? 
15:11 But we believe that we are saved through the grace of the Lord Jesus,
{TR adds "Christ"} just as they are." 

"Brothers, listen to me. 
15:14 Simeon has reported how God first visited the Gentiles
, to take out of them a people for his name. 
15:15 This agrees with the words of the prophets. As it is written, 
15:16 'After these things I will return. I
will again build the tent of David, which has fallen.
I will again build its ruins. I will set it up, 
15:17 That the rest of men may seek after the Lord; 
All the Gentiles who are called by my name, 
Says the Lord, who does all these things. (Amos 9:11,12)
15:18 All his works are known to God from eternity.' 
15:19 "Therefore my judgment is that we don't trouble those 
from among the Gentiles who turn to God, 
15:20 but that we write to them that they abstain from the pollution of idols, 
from sexual immorality, from what is strangled, and from blood. 
15:21 For Moses from generations of old has in every city those who preach him, 
being read in the synagogues every Sabbath."  

vs 5 Luke writing in an historic sense speaks of these Pharisees as "believers" referring simply to their association with the Christian community. But Paul writes of this incident in Galatians 2 saying

"Yet not even Titus, who was with me, was compelled to be circumcised, even though he was a Greek. This matter arose because some false brothers had infiltrated our ranks to spy on the freedom we have in Christ Jesus and to make us slaves. We did not give in to them for a moment, so that the truth of the gospel might remain with you."Gal 2:3-5

The church of Jerusalem had false brethren infiltrating the ranks whose objective was to change the gospel so as to bring the Christian community under the bondage of the Law as they saw it. And there are many such people even today in the Christian community. What I find interesting is that the leaders of that church - James, Peter and John apparently were either unaware such infiltration was going on, or simply not willing to deal with it until Paul has to finally come to deal with it himself. Such false brothers would certainly not have been tolerated as far as Paul was concerned. The weakness of the leaders of the Jerusalem church was again evident in Galatians as Paul rebukes Peter.

"When Peter came to Antioch, I opposed him to his face, because he was clearly in the wrong.  Before certain men came from James, he used to eat with the Gentiles. But when they arrived, he began to draw back and separate himself from the Gentiles because he was afraid of those who belonged to the circumcision group." Gal 2:11,12

vs 7-11 Peter makes reference to Acts 10 in which he preaches to Cornelius, a Roman centurion. This dispute should have been put to rest long before when Cornelius was converted. For I don't perceived that he was required to be circumcised after his conversion. In fact I wonder what happened to him. For though living in Israel it doesn't appear that he being uncircumcised would be welcomed into the church at Jerusalem. Furthermore despite Peter defending Paul on the matter, we can see an "us" versus "them" mentality when he speaks of Gentile believers, except for in verse 10 when he simply refers to them as "disciples". I wonder if in reality Peter was not as prejudice as he appeared, but rather was simply using figures of speech acceptable to the racist Jews.

Peter's Argument:
Verse 10-11 is the crux of Peter's argument declaring that their proposition is not consistent with what God has revealed and that they are burdening the church with their human dogma. For salvation is not dependent upon rituals, but upon the grace of God.

vs 12 Paul & Barnabus' Affirmation:
Just as the miracles done by Paul and Barnabus had affirmed to the Gentiles that they were speaking for God. So also this same evidence can be used to affirm their doctrine of salvation by grace against the cult of the circumcision. 

vs 13-21 James's Argument:
James references the Scriptures, affirming that this turning of the Gentiles to God is consistent with prophecy. Implicit in his reasoning is that the scriptures don't refer to Gentiles becoming Jews, but rather Gentiles as Gentiles worshipping God.

vs 16 James references the prophet Amos. The prophecy was given before Israel's Assyrian captivity. One might view the literal fulfillment took place when Zerubbabel returned from captivity to rebuild the temple in accordance with the commission of Cyrus King of Persia. The restoration of Israel to the promise land prepared an environment in which the Messiah would come. Having come he established his people and now the he was drawing the Gentiles to God. Or viewing it more spiritually one might say that the rebuilding of the tabernacle of David was the building of the Christian church into which Gentiles had now been introduced. The gist of this is that God is doing a work as was foretold and let's not interfere.

vs 19-20 Why does James seem to have the final word? He was never commissioned as an apostle to begin with. During Jesus' ministry he didn't believe (John 7:5), and even at one point reckoned Jesus crazy. (Mark 3:21) But Jesus had appeared to him after the resurrection (1Cor 15:7), during which he may have given him instructions and a position of authority. But we just don't know that. Furthermore his judgment seems self-contradictory. For after saying that they should not burden the Gentiles with additional requirements he then goes on to burden the Gentiles with additional requirements. 

• abstain from food polluted by idols, 
• from sexual immorality, 
• from the meat of strangled animals 
• and from blood.

Matthew 15:
11 What goes into a man's mouth does not make him 'unclean,' but what comes out of his mouth, that is what makes him 'unclean.'"
17  "Don't you see that whatever enters the mouth goes into the stomach and then out of the body?
18  But the things that come out of the mouth come from the heart, and these make a man 'unclean.'
19  For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander.'

He furthermore nullified the dietary commandments in Peter's vision which was in reference to Gentile believers, commanding "Do not call anything impure that God has made clean." Acts 10:15 Although not explicitly referring to meats sacrificed to idols, strangled animals, and blood. But the principle applies. For Paul goes on to write:

"As one who is in the Lord Jesus, I am fully convinced that no food is unclean in itself. But if anyone regards something as unclean, then for him it is unclean." Romans 14:14

Is James saying that the Gentiles don't have to be circumcised and follow the Law to be saved, but they must do these other 4 things? If so then his position is not much different than that of the cult of the circumcision. But on the other hand these four conditions might not be referring to conditions for salvation, but rather conditions for fellowship with Jewish brethren.  Such an interpretation would also be consistent with Paul's writings on the matter given above. For Paul does carefully instruct the Gentiles to be sensitive the conscience of the weaker brethren, which would include many Jews who grew up under the Law and as such developed a scruples concerning foods and other symbolic matters as the Law of Moses instructed. But then again if that is the case, then why did he include sexual immorality? For sexual immorality is not a gray area. It is absolute and must be avoid regardless of how people feel. 

"It is God's will that you should be sanctified: that you should avoid sexual immorality." 1Thess 4:3
"Food for the stomach and the stomach for food"-- but God will destroy them both. The body is not meant for sexual immorality, but for the Lord, and the Lord for the body." 1Cor 6:13 
"But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God's holy people." Eph 5:3

vs 21 The "for" statement supports his proposal. He was saying that since the Law of Moses was being preached throughout the Jewish community, undoubtedly Jews have developed many scruples concerning foods and such, to which Gentiles need to be sensitive so as to not defile their conscience. 

This may be likened to the following scenario. Imagine at time in which the preaching again alcohol or dancing or such things was prevalent. Christian develop certain scruples concerning these, even though being gray areas. Now suppose someone from outside that society who hadn't grown up with such scruples is converted. How should such a convert behave among those with the scruples? Though he himself has may have no problem with these things, yet he needs to be sensitive to the conscience of others so as not to defile them. 

But on the other hand comes the issue of legalism in which such scruples are viewed as conditions for salvation. That is likened to the cult of the circumsion who viewed circumcision and obedience to the Law of Moses as prerequisites to salvation. That's a much different matter. To them Paul says, "If anybody is preaching to you a gospel other than what you accepted, let him be eternally condemned!" Gal 1:9