For the law of Moses has been preached in every city from the earliest times and is read on the synagogue every Sabbath.
This statement is explaining why the Noachide laws are still valid and should not be a surprise: they have been preached from ancient times in every city. Everyone in the ancient world understands what Jews claim to be universal to all mankind.
Furthermore (and some scholars expand this one too far in my opinion and make it the main point), because this is known to every Jew, it is particularly offensive to see Gentiles claim to share in the blessings of God and not follow them. So by choosing to obey these laws, the Gentiles are also building a bond with their Jewish brethren. However, this seems to be the lesser of the two meanings and should not be expanded too far into theology, lest .
Then the apostles and elders, with the whole church, decided to choose some of their own men and send them to Antioch with Paul and Barnabas. They chose Judas called Barsabbas and Silas, men who were leaders among the believers.
The Elders and Apostles did not want to take any risk of Paul and Barnabas not being believed when they returned to Antioch. Therefore they took leaders from among the church body, who we are told later also are members of the preaching group, and send them to ensure the message is communicated properly.
With them they sent the following letter: To the Gentiles believers in Antioch, Syria, and Cilicia: Greetings.
First and foremost, they identify the Gentiles as believers. They use the same word (adelphos) to describe the believers in the Gentile regions as they do their own believers; calling them brethren in Christ.
We have heard that some went out without our authorization and disturbed you, troubling your minds by what they said.
They clearly refute the claims of the Judaizers to have come from James, and mention that the things that they were told troubled their minds.
So we all agreed to choose some men and send them to you with our dear friends Barnabas and Paul
Here they affirm the legitimacy of the current messengers as well as letting the churches know that Barnabas and Paul are “dear friends” whom they support.
--men who have risked their lives for the name of Jesus Christ.
They reiterate that the men from their congregation whom they are sending are bold followers of Jesus and can be trusted to deliver the message.
Therefore we are sending Judas and Silas to confirm by word of mouth what we are writing.
Two-thirds of the letter written to them was to secure authority in the messenger. This fact reinforces that it was very unclear to the Gentiles whom they could trust. Two sets of missionaries show up, both claiming the authority of the apostles…there is no Scripture at the time to consult…so how will they know who is teaching God’s word and Gospel?