Well…you can’t get much earlier than the apostle Paul on the subject. The emphasis was on the resurrection. Paul wrote, in effect, that unless there is a resurrection, we may as well eat, drink, and be merry, for there would be nothing more.
…If the dead are not raised, let us eat and drink, for to-morrow we die. (1Corinthians 15:32 ASV)
I have found that other early Christian writers throughout the centuries who wrote of the afterlife also indicated the resurrection to be the all-important aspect of the afterlife.
Later, when the idea of going to heaven immediately after death caught on, “resurrection” was redefined to mean the “soul” or “spirit” being raised immediately after death or continuing to live through death, and going to heaven right away.
I recall attending two funerals in one day. In the morning, the speaker at the funeral said, “Mr. H will live again!” When he said that a kind of thrill went through my being. It seemed to be a glorious truth!
In the afternoon, the speaker at the funeral said, “Mrs. K did not die. She just walked through a door.”
To me this did not sound like a statement that described reality. It sounded like a fairy tale.