What was the first New Testament Scripture? It was one of Paul’s letters, probably Galatians or Thessalonians. This was written within 20 years of Jesus’ resurrection, around AD 48:
1 & 2 Thessalonians 1:1 (my translation, compare NIV)
Paul and Silas and Timothy, to the assembly of Thessalonians in God our Father and our Lord Jesus his anointed. Grace to you, and peace.
Did you notice the unusual address? In later letters Paul wrote to the church in Corinth or in Philippi. What did he mean by writing to the Thessalonians in God?