The apostle again identifies the event around which his thoughts are revolving, namely, the coming of the Lord in glory (cf. v. 7).

 That is, to be glorified in the persons of His saints. The supreme vindication of Christ‘s ways will take place when the whole family of His saints is gathered together. Then the universe will see the value of His sacrifice and the success of the course He pursued. Thus the Saviour will be glorified (cf. Gal. 1:24; 1 Thess. 2:20; 2 Thess. 1:4). As the artist is glorified in his masterpiece, so Christ is glorified before the heavenly throng by His handiwork—the miracles of His grace (see Matt. 13:43; TM 18, 49, 50). Throughout eternity glory will redound to the Saviour as His saints make known more fully the wisdom of God in His wondrous plan of salvation, which has been “realized in Christ Jesus our Lord” (Eph. 3:10, 11, RSV).

 Gr. thaumazō, “to wonder,” “to wonder at,” “to marvel”; in a secondary sense, “to admire.” Both senses appear in the text. The saints have eagerly awaited their Deliverer, they have joyfully anticipated His appearing, but the realization of their expectations far exceeds their most sanguine hopes. They never dreamed their Lord could be so glorious. When the beauty of His presence has dawned upon them, to their wonder is added a reverent admiration (see Isa. 25:9).

Or, “by all.”

 Literally, “who have believed,” or “who have fixed their faith.” It is those who fixed their faith before Christ‘s coming who are saved “in that day.” It is those who have already accepted their Lord by faith, and who have endured to the end, who will be saved when Jesus returns (Matt. 24:13). Paul particularly had in mind his Thessalonian converts and their initial act of belief in the gospel, as is made clear from the parenthetical expression “because our testimony among you was believed.” They had become transformed as they accepted the message of salvation, and were assured that, if they were faithful, they would also be among the saints. But the phrase “all them that believe” also applies to all faithful believers.

 The apostles bore witness to the great truths of the gospel (Acts 1:8; 2:32; 8:25; 1 John 1:1, 2). They did not preach abstract discussions, finespun theories, or “cunningly devised fables” (2 Peter 1:16). Rather, their preaching was the testimony of eyewitnesses. These truths they knew experimentally, and they urged the acceptance of a way of life which they themselves lived. Such preaching always has power.

 Ambiguity is avoided if this phrase appears earlier in the verse, after “when he shall come,” or following “his saints.” For comment on “that day” see on Acts 2:20; cf. on Phil. 1:6.