The language of 1 Thessalonians 2:10 creates a picture of the ancient courtroom, where two or more witnesses were required to validate a person’s testimony (see Deuteronomy 19:15; 2 Corinthians 13:1). The tone is solemn, and shows that Paul believes he is dealing with a life-and-death matter; it is crucial for the Thessalonians to accept as true what Paul is about to say.1,2 Thus he appeals to witnesses whom they must find persuasive: you are witnesses, and so is God.
10 You are witnesses, and God also, how holy and righteous and blameless was our conduct toward you believers.