"You are all sons of light and sons of the day. We are not of the night nor of darkness."
Notice that Paul tells *all* the faithful Thessalonian churchmen (who were in good standing)--be they young or old--that they are "sons of light and sons of the day." I'm sure that all of them--just like faithful churchmen today--did not *feel* like "sons of light," because of the continuous knowledge of sin, temptation, and various imperfections.
Nonetheless, they still *were* "sons of light," even as faithful churchmen today are, as well. And why? Because Jesus, the True and Perfect Light is in and among them. His light makes us children of light.
[Puritan quote of the day: "There is nothing in the world so glorious as a grown Christian." --Richard Sibbes, in "Glorious Freedom"]