The letter and messengers encouraged the believers at Antioch.

Acts 15:30-32

30 The four men whom they had chosen went from Jerusalem to Antioch city. When all the believers there had assembled together, Judas and Silas gave the letter to them. 31 When the believers there read the letter, they rejoiced, because its message encouraged them. 32 Just like Paul and Barnabas were ◄prophets/men who spoke messages from God►, Judas and Silas were also prophets. They spoke for a long time and encouraged the believers there, and helped them to trust more strongly in the Lord Jesus.