and sent Timothy, our brother and God's servant in the Gospel of Christ, to establish you, and to comfort you concerning your faith;
There were several reasons for sending Timothy (or Silas) to visit the Thessalonians.  Not only was Paul most urgently concerned in knowing how they were doing and in receiving the encouragement which a good report might provide, there would also be definite benefits to the Thessalonians as well.  They would be: (1) established and (2) comforted.  They needed both.  Young converts facing a storm of persecution might fall away unless established and comforted.