Timothy was sent to visit the Thessalonians Church (v1-5)
The history of Paul’s missionary journey from Philippi to Thessalonica to Bereas to Athens and finally to Corinth was recorded in Acts chapter 17 and 18.
Paul, together with with Silas and Timothy, were in Berea preaching the gospel, but when the Thessalonica Jews learned about their work there, they came to agitate the crowds to stir up trouble to Paul, Silas and Timothy (Act 17:13). So The Berea brothers immediately sent Paul to Athens, but Silas and Timothy stayed in Berea. Paul left with instruction for Silas and Timothy to join him in Athens as soon as possible (Acts 17:15).
It is likely that Silas and Timothy joined with Paul in Athens not too long after that. It was at Athen where Paul and Silas were thinking about the Thessalonians Church and sent Timothy to strengthen and encourage them in their faith (1 Thes 3:2). It was possible that Paul later sent Silas to visit the Macedonia church also since Acts 18:5 recorded that Silas and Timothy came from Macedonia to join with Paul.
Unlike other cities, Paul did not receive persecution in Athens. After he preached the gospel to the Athenians, and many believed in Christ, and then Paul left Athens to Corinth (Acts 18:1).
After Timothy finished visiting Thessalonica, he and Silas came to join Paul in Corinth (Acts 18:5, 1 Thes 3:6).
The reason why Paul wanted to sent Timothy to visit the Thessalonica church was because they were under trials (3:3), being tempted by Satan (3:5).
Paul was worried that this young church could unsettled by these trials (3:3). He knew they needed the encouragement from more mature Christians.
Report from Thessalonica (v6-13)
Timothy brought back good report from his visit to Thessalonica (Acts 18:5, 1 Thes 3:6).
Their faith in Christ has encouraged Paul (v7). Often times, the faith of young believers is great encouragement for Christians workers.
v8: [..standing firm in the Lord]. After we shared the gospel and people believed. We desire them stand firm in the Lord.
v10: [Night and day we pray..]. Do we pray for the people we minister do?
v12: […love increase and overflow..]. The sign of Christians is our love for each other and for the everyone else.