The blessed expectation of our Lord's return before the day of His indignation is the subject of these, Paul's earliest epistles. It is the early opening wedge between those who received his ministry among the nations and those of the Circumcision, who looked for Messiah's advent after the display of His indignation and the destruction of man's kingdoms.
The historical background for this change is given in the book of Acts, though the doctrine itself is not found there because the Acts is a treatise on the kingdom of God for Israel. In the ministry of our Lord and His twelve apostles, His coming is always presented in its connection with the promised kingdom. It will be with power and great glory (Mt.24:30; Mk.13:26; Lu.21:27). His feet shall stand on the Mount of Olives (Acts 1:11-12; Zech.14:1-5). All the predictions in the book of Daniel and in the Revelation of Jesus Christ will find fulfillment from then on. It will follow an era of the most awful and terrific judgments mankind will ever be called upon to endure. So long as the kingdom was impending these judgments, also, were hanging over a rebellious race.
At first Paul, like all the rest, confined his ministry to the Jews. At Antioch, where the disciples were first called "Christians," there were none except Jews and proselytes. From this, he was separated (Acts 13:2). At Pisidian Antioch he first turned to the nations, or Gentiles. After that, though he spoke to the Jews first, he proclaimed Christ freely among the nations, preaching grace. One of the first questions for these believers among the nations was, What shall become of us in the great judgments which precede the coming of the kingdom? Will God pour out His bowls of wrath upon our heads? In answer to this, the apostle is given an entirely new revelation concerning the future presence of the Lord. The believers among the nations were saved on the ground of grace. This is to characterize all God's dealings with them. Hence they cannot remain in the scene which is visited by His indignation. They must be sheltered or removed. Some saints in Israel are sheltered, but the new company, composed principally of saints from the other nations who have believed Paul's preaching, are to be removed. Paul receives the revelation that, long before the Lord descends in glory to set up His kingdom, He will descend, not to the earth, but to the air, and His saints will be caught up to meet Him there. Thus they will be above the lightnings and thunders of the terrible day of the Lord.
In later epistles, as the truth was gradually developed, more details were added to this glorious revelation. The Corinthian mind found difficulties in this doctrine, so the apostle unfolds to them the secret or mystery of the resurrection (Co.15:51-52), that our bodies, which, at present, are adapted only to an earthly environment, are to be changed to suit the celestial spheres. The Philippian letter caps the climax by the added revelation that they shall be transfigured into the glorious likeness of our Lord Himself!