John Chrysostom, on 1Thess 1:7

"So that ye became ensamples to all that believe in Macedonia and Achaia."

And yet it was later that he went to them. But ye so shone, he says, that ye became teachers of those who received (the word) before you. And this is like the Apostle. For he did not say, so that ye became ensamples in regard to believing, but ye became an ensample to those who already believed; how one ought to believe in God, ye taught, who from the very beginning entered into your conflict. "And in Achaia," he says; that is, in Greece. Do you see how great a thing is zeal? that it does not require time, nor delay, nor procrastination, but it is sufficient only to venture one's self, and all is fulfilled. Thus then though coming in later to the Preaching, they became teachers of those who were before them.

Let no one therefore despair, even though he has lost much time, and has done nothing. It is possible for him even in a little while to do so much, as he never has done in all his former time. For if he who before did not believe, shone so much at the beginning, how much more those who have already believed! Let no one, again, upon this consideration be remiss, because he perceives that it is possible in a short time to recover everything. For the future is uncertain, and the Day of the Lord is a thief, setting upon us suddenly when we are sleeping. But if we do not sleep, it will not set upon us as a thief, nor carry us off unprepared. For if we watch and be sober, it will not set upon us as a thief, but as a royal messenger, summoning us to the good things prepared for us. But if we sleep, it comes upon us as a thief. Let no one therefore sleep, nor be inactive in virtue, for that is sleep. Do you not know how, when we sleep, our goods are not in safety, how easy they are to be plotted against? But when we are awake, there needs not so much guarding. When we sleep, even with much guarding we often perish. There are doors, and bolts, and guards, and outer guards, and the thief has come upon us.