Adam Clarke on 1 Corinthians 15:51

I show you a mystery - That is, a thing which you have never known before. But what is this mystery? Why, that we shall not all sleep; we shall not all die; but we shall all be changed: of this the Jews had not distinct notions. For, as flesh and blood cannot inherit glory, and all shall not be found dead at the day of judgment, then all must be changed - undergo such a change that their bodies may become spiritual, like the bodies of those who shall be raised from the dead.