The New Testament barely ever talks about “going to heaven when we die,” but it talks a lot about the hope for bodily resurrection to everlasting life in a renewed and glorified creation. Yet the popular understanding today is that “going to heaven” is the central promise of the Christian Gospel.

How did this happen? Well, it was a long and involved process of historical development, but here is a simplified summary:

1. As Christianity spread beyond the Mediterranean to the Franks, Goths, Celts, etc., of Europe, theological attention to the resurrection hope faded in favour of hope for a heavenly afterlife. Unlike the Greeks, Jews, Egyptians, Mesopotamians, etc., who believed that all the dead descended to an underworld of some sort, these peoples tended to believe that at least some people (e.g. brave warriors) would be taken to the heavenly dwellings of the gods. Whether by intentional evangelistic strategy or by steady cultural osmosis, the focus of both theology and popular piety shifted from resurrection by the grace of God in Christ to going to heaven through the grace of God in Christ.
2. This became entrenched in the Middle Ages as the veneration the saints became established and spread, since such veneration and the associated practices only made sense if the saints were both enjoying the full blessedness of heaven and fully aware of events transpiring on earth.
3. After one medieval Pope tried to correct the distortion and earned for himself a whole bunch of infuriated pushback, the next Pope issued an edict that rejected what the previous Pope had taught and instead made it official church teaching that each person after death faces “particular judgement” to determine their fate, upon which they are sent either to hell, purgatory, or (if one was already holy enough) straight to heaven.
4. The Protestant reformers rejected the purgatory element that official Catholic doctrine taught, but most kept the rest of the rest of the framework. (Luther notably rejected the whole thing and instead taught that the dead essentially sleep until the resurrection. However, he was not followed in this by later Lutherans.)

Throughout all of this no theologians who were even remotely orthodox ever rejected the hope for resurrection and cosmic transformation when Jesus returns. The problem was rather that the final hope was relegated to the status of a nearly forgotten appendix. As more and more of the theological work that rightly belongs to the resurrection hope was transferred to a hope for a blessed disembodied existence in heaven, preachers and teachers found less and less reason to talk about the resurrection, and so the public came to believe that going to heaven when they died was the entire hope.