But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep. (1 Cor 15:20)
Christ is the "firstfruits of those who have fallen asleep." This is a harvest picture. "Firstfruits" is not only the beginning of the crop, it also demonstrates the reality of the crop. Is eternal life possible? Before Christ, who knew? Afterwards, we know absolutely. He is the firstfruits, the evidence that such a crop exists.
For since death came through a man, the resurrection of the dead comes also through a man. For as in Adam all die, so in Christ all will be made alive. (1 Cor 15:21-22)
Christ is the guarantee of the resurrection of the believing dead to a life that is eternal (1 Cor 15:21-22). Comparing Adam and Christ, Paul writes that just as those who are in Adam die, those who are in Christ will be made alive. So, everyone connected with Adam die. We know that. We all know that sometime, unless Christ comes back soon, we will come to our last breath. And as sure as death is, those of us who are in Christ are also sure that we will be made alive. We will be raised to an eternal life.
But someone may ask, "How are the dead raised? With what kind of body will they come?" ...
The body that is sown is perishable, it is raised imperishable; it is sown in dishonor, it is raised in glory; it is sown in weakness, it is raised in power; it is sown a natural body, it is raised a spiritual body.... The first man was of the dust of the earth, the second man from heaven. As was the earthly man, so are those who are of the earth; and as is the man from heaven, so also are those who are of heaven. And just as we have borne the likeness of the earthly man, so shall we bear the likeness of the man from heaven. (1 Cor 15:35, 42-44, 47-49)
We will be equipped for the new kind of life, for eternal life. We will be raised in resurrection bodies. That is to say, we will have new bodies that are different than what we have now. Different in what way? Descriptions are not specific, but the characteristics listed should give hope: "imperishable," "glory," "power," "spiritual" (as opposed to "natural").