http://bible.org/seriespage/1-thessalonians-213-and-emerging-canon-consciousness
“And so we too constantly thank God that when you received God’s message that you heard from us, you accepted it not as a human message, but as it truly is, God’s message, which is at work among you who believe” (NET).
There’s an interesting discussion here about whether Paul knew that he was writing “scripture” – as in, what would become scripture, and carry the same weight as the OT canon. The author makes the point that if he does, then this is the first indication that the apostles are writing in a self-referential style. However, the phrase “God’s message” or “God’s word” also refers to the teaching that the apostles were doing, which was not the written word of the OT but instead their testimony about the life of Jesus and the Kingdom of God.