After reaching the epic decision, by the Spirit, that Gentiles are not to be required to come under the Law, and that salvation is indeed truly by grace alone, the Jersualem church send a letter to Antioch (15:30), which is also subsequently taken on around Galatia (16:4) (showing that the judgement wasn't just for one church but vital for all the churches).
But they didn't just send a letter, they sent two respected leading men, Barsabbas and Silas. I think this is exemplary. They took every effort:
1. to encourage the Gentile believers
2. sending authorised personal representatives who could personally clear up any misunderstandings and distance themselves from the previous unauthorised teachers who had troubled the minds of the Antioch believers
3. provide for the spiritual needs of the new believers. We are told that Barsabbas and Silas were prophets who strengthened and encouraged the brothers with many words (15:32)
4. to make sure that Paul and Barnabas and their message of grace were affirmed. If they had returned on their own saying "we checked things out with the folk in Jerusalem and they are fine with the message we have been preaching" there would be no independent verification. The Jerusalem church provide that through Barsabbas and Silas
Where there has been misunderstanding between believers it is a good thing to put things personally, not impersonally. A letter on its own sometimes isn't enough, especially if there has been personal hurt or doctrinal confusion. Let's do it like the Jerusalem church did it, making every effort to maintain the unity of the Spirit in the bond of peace.