For we know, brothers loved by God, that he has chosen you, (1 Thessalonians 1:4 - ESV)
Once again, Paul directs his praise all toward God. These Thessalonians that are displaying Faith, Love, and Hope through their Work, Labor, and Steadfastness... They are Loved by God.
Now, ask the question, "Are they loved by God because of their displays of Faith, Hope, and Love? Or are they displaying these things because they are loved by God?"
I believe that the answer is obvious for two reasons. Consider first that Paul is thankful TO God for the Faith, Hope, and Love of the Thessalonians. He is not thanking the Thessalonian people for these things, he is thanking God! And if there is any question, consider also that final statement in this verse: that God has CHOSEN them! What a great reality this is.