The Timing of Gentiles in the Body of Christ in Relation to 1 Thessalonians 4:14

Your question touches the heart of how one understands the timing of the body of Christ and the right division of Scripture. 1 Thessalonians 4:14 is within a passage that clearly addresses the hope of believers at the Lord's coming. The issue is whether, by the time 1 Thessalonians was written, Gentiles had already been incorporated into the body of Christ.

Broadly speaking, Christian interpreters fall into several camps:

1. No real distinction, no right division. The vast majority of Christians effectively treat God's people as one continuous entity across Scripture. For them, the "church" (in their sense) spans from at least Pentecost, and often functionally from Abraham or earlier. In that framework, Gentiles are obviously present throughout the New Testament era. For such interpreters, your question barely arises.
2. Church begins at Pentecost, all Pauline letters to the same entity. A smaller but significant group holds that the body of Christ (the "church") begins in Acts 2, at Pentecost. In this view, by the time Paul writes 1 Thessalonians (around A.D. 50), the body of Christ, including Gentiles, is well-established. Again, the default answer in this model would be a simple "yes."
3. Church begins with Paul; Romans--Philemon uniformly to the body of Christ. A still smaller group sees the body of Christ originating with Paul's distinctive apostleship and message (Acts 9--13 or so). Within this camp, most would treat all of Paul's epistles, including 1 Thessalonians, as written directly and exclusively to the body of Christ. They would likewise answer "yes," assuming Gentiles in the body by the time of 1 Thessalonians.
4. Acts 28 position. An even more distinct group situates the full beginning of the body of Christ's dispensation at Acts 28. From that vantage point, earlier Pauline letters (including 1 Thessalonians) are often seen as still operating within an Israel-centered framework. An Acts 28 interpreter might say that 1 Thessalonians 4:14 relates primarily to Israel's hope and not to a fully formed Gentile body of Christ, or would carefully distinguish those "grafted in" from the ultimate church of the mystery.
5. Overlap view (body of Christ beginning with Paul, but with a transitional overlap). The position I am articulating sees Paul as the apostle through whom the body of Christ and the gospel of grace are introduced, yet recognizes a transitional overlap period in Acts. During that time, there are believing Jews who belong both to the "little flock" of kingdom heirs and to the body of Christ through belief in Paul's message. The destruction of Jerusalem marks the effective end of this overlap.

From this overlap perspective, 1 Thessalonians was written after the Acts 15 council, by which time:

• Paul's Gentile mission was already well underway.
• The distinctiveness of his message to the Gentiles was acknowledged, even if not fully understood by all.
• Local assemblies, such as in Thessalonica, likely contained both Jews and Gentiles, though in Thessalonica's case the recipients appear predominantly Jewish-background in the narrative of Acts.

Therefore, yes, there were Gentiles in the body of Christ by the time Paul wrote 1 Thessalonians. Moreover, the rapture passage of 1 Thessalonians 4 is applicable to the body of Christ, which by then includes Gentiles. That said, within 1 Thessalonians itself there are sections that appear more directly oriented toward a Jewish audience and kingdom-related themes, especially earlier chapters. A careful right division within Paul's letters recognizes both the Jewish overlap context and the emerging truth of the body of Christ.

In other words:

• The body of Christ, including Gentiles, existed when 1 Thessalonians was written.
• 1 Thessalonians 4:13--18 properly describes the hope of that body.
• Yet Paul wrote in a historical moment when Jewish kingdom believers and the new body of Christ overlapped, and both realities must be kept in mind when interpreting his earliest letters.