Pretribulation interpreters maintain there is a difference in meaning between the terms the day of the Lord and the day of Christ.
The term the day of Christ (Phil 1:6, 10; 2:16) has been thought to refer to the rapture and not God’s wrath, while the day of the Lord is believed to refer to a different time period concerned only with God’s wrath. (Incidentally, the KJV in 2 Thess 2:2 has the reading “the day of Christ,” but the earliest and best manuscripts overwhelmingly attest to “the day of the Lord.”*)
Both terms, however, should be understood to refer to the same event, being interchangeable designations for the unified complex-whole of Jesus’s return. To be sure, this does not mean that their respective contexts cannot constrain a certain aspect of Christ’s return such as, for example, focusing on the beginning point when the saints will meet Christ. Nor does it mean that they share the exact same connotation. No two words share the exact same connotation; but many words can refer to the same event, thing, or concept.
It will be argued here that the day of the Lord includes the day that the rapture occurs; consequently, the distinction between the day of Christ and the day of the Lord is inconsequential to the rapture question, and thus should not be considered evidence for a pretribulation rapture. The following reasons support that both these terms co-referentially denote the same event of our Lord’s return.
1. The Lord is Christ. The apostle Paul uses “Lord” for “Christ” innumerable times, and interpreting Old Testament prophecies concerning the day of the Lord to be about Christ is no exception. Thus, Paul had the freedom, especially as we see in Philippians, to interchange “Lord” for their new messianic understanding in “Christ” or “Jesus.” A conflation of the two terms is found in 1 Cor 1:8: “He will also strengthen you to the end, so that you will be blameless on the day of our Lord Jesus Christ” (cf. 1 Cor 1:7!) and 2 Cor 1:14: “day of the Lord Jesus.” These four variations do not denote four different periods! Robert H. Gundry (Church and the Tribulation, 98) makes the point that “if mere differences in titles and names justified distinctions, we ought to distinguish between ‘the judgment-seat of God’ (Rom. 14:10) and ‘the judgment-seat of Christ’ (2 Cor . 5:10). Yet no one thinks of doing so.”
2. In 2 Thess 2:1–2, Paul does not view a temporal separation but rather links the gathering of the saints to Christ happening when the day of the Lord begins: “Now regarding the coming of our Lord Jesus Christ and our being gathered to be with him [the rapture], we ask you, brothers and sisters, not to be easily shaken from your composure or disturbed by any kind of spirit or message or letter allegedly from us, to the effect that the day of the Lord is already here.”
3. In 1 Thess 5:4, Paul teaches that believers will be here on the first day when the day of the Lord begins: “But you, brothers and sisters, are not in the darkness for the day to overtake you like a thief would.”
Then in 1 Thess 5:6–9, he instructed believers to watch for the day of the Lord, because it will be salvation for saints living at that time but judgment for the world:
“So then we must not sleep as the rest, but must stay alert [grēgoreō] and sober. For those who sleep, sleep at night and those who get drunk are drunk at night. But since we are of the day, we must stay sober by putting on the breastplate of faith and love and as a helmet our hope for salvation. For God did not destine us for wrath but for gaining salvation through our Lord Jesus Christ.”
It would not make sense for Paul to instruct the Thessalonians to “watch” for the day of the Lord if the saints have already been raptured to heaven.
In addition, Paul reassures the Thessalonians that when the day of the Lord begins, all saints “whether we are alert [alive and watching] or asleep [dead in Christ] we will come to life [resurrection] together with him [raptured]” (1 Thess 5:10; cf. 1 Thess 4:14–18).
The last generation of the church therefore will be here to witness the day that the day of the Lord begins. The terms the day of Christ and the day of the Lord are synonymous, denoting the one and same period of the Lord’s return, which will include the rapture and the pouring out of God’s wrath upon the world. The apostle Paul had the freedom to interchange these terms. As I noted at the beginning, the connotations have a slight nuance—as all terms possess—but the referential identity is the same.