 He's dealing, of course, with the second coming of the Lord. The word that Paul uses here is very interesting. When he talks about the return between believers and unbelievers, it's fascinating. He never uses the same word for each group. And that's on purpose, of course. When he's talking with believers about the return of Christ, about the arrival of Christ, he uses a completely different word than the word that is used here when he shall be revealed.