What will happen to our bodies? What goes into heaven? Paul’s answer: spiritual bodies. Our physical bodies (our flesh) never gets to leave earth:
1 Corinthians 15:50 What I am saying, dear brothers and sisters, is that our physical bodies cannot inherit the Kingdom of God. These dying bodies cannot inherit what will last forever.
But that’s not the end. Just as Jesus was raised from the dead, so will we be:
1 Corinthians 15:51-53 But let me reveal to you a wonderful secret. We will not all die, but we will all be transformed! It will happen in a moment, in the blink of an eye, when the last trumpet is blown. For when the trumpet sounds, those who have died will be raised to live forever. And we who are living will also be transformed. For our dying bodies must be transformed into bodies that will never die; our mortal bodies must be transformed into immortal bodies.
This happens, as Paul said, when the last trumpet is blown. He has also described the same event to the Thessalonians, encouraging them that Jesus would come back for them.
John also described a seventh (and final) trumpet in Revelation 11:15-18, when Jesus returns with judgement (poured out from seven bowls).
Jesus also described a trumpet being used to gather His people from the ends of the earth when he returns at the end:
Matthew 24:30-31And then at last, the sign that the Son of Man is coming will appear in the heavens, and there will be deep mourning among all the peoples of the earth. And they will see the Son of Man coming on the clouds of heaven with power and great glory. And he will send out his angels with the mighty blast of a trumpet, and they will gather his chosen ones from all over the world—from the farthest ends of the earth and heaven.
But Jesus made it clear: no one could say when this would happen:
Matthew 24:36 However, no one knows the day or hour when these things will happen, not even the angels in heaven or the Son himself. Only the Father knows.
The context for this would have had to have been the scriptures that we now call the Old Testament (there was no New Testament then). They all would have known, and participated in, the Feast of Trumpets that God commanded through Moses:
Leviticus 23:24-25 Give the following instructions to the people of Israel. On the first day of the appointed month in early autumn,you are to observe a day of complete rest. It will be an official day for holy assembly, a day commemorated with loud blasts of a trumpet. You must do no ordinary work on that day. Instead, you are to present special gifts to the Lord.
Although no reason for the feast is given in the Law, it’s held by tradition to be a day to reflect on our own spiritual welfare before God—to repent so we can stand in God’s judgement (held 10 days later, on the Day of Atonement).
Later tradition added it as an anniversary of creation of Adam and Eve, and their later fall and repentance, followed by receiving God’s forgiveness (which Christian tradition sees in Jesus). On the same day, Abraham obeyed God and moved to sacrifice Isaac (but sacrificed a ram, caught by its horn, instead); Jacob purified himself and his family before meeting up with Esau again.