Try this thought experiment. It's sometime before the Crucifixion and you are in Hades. Okay, so Hades is a metaphor for being dead. We use the metaphor because it makes talking about being dead much easier. Otherwise it's usually too hard to conceive and too elusive for words.
So, there you are, in Hades, alone or dimly aware of the others there. You are aware, but you have no body, hence no brain, informing you that you are aware. You have, in other words, no reflexive, or double consciousness. It's dark, both physically (you have no eyes) and spiritually (you don't perceive any sign of God). Your body has rotted away and your soul is fading out, as well - very, very gradually (for God was not about to let you enter into total oblivion, so He slowed down that process until the time should come to rescue you).
And then a miracle happens. Suddenly, you have some new way of seeing and hearing, even without your body. Your reflexive consciousness, without which you were less than human, is back again. Though you have no eyes, you see a Light more beautiful and more brilliant than you could ever have imagined or could ever describe, and in the midst of this Light, the form of a Man, of a Liberator. You are engulfed by an almost palpable, strong wave of Love. You realize you are not the only one. You are no longer alone, and the Light and the Love and the New Life are flooding over all the others, too. You know you did evil during your lifetime, but you also now know, beyond any doubt, that all is forgiven.
Christ has entered Hades. Your heart is singing, and weeping, and dancing for joy, for love. You are overcome with gratitude.
* * *
So here's the question: is this still Hades?
Christ Jesus, by His Presence there, has made it into Paradise. Permanently. Hades remains filled with His Holy Spirit; by Whom you are able to "see" and "hear" even without a brain. It's the fulfillment of what Prophet King David wrote: "If I descend into Hades, behold, Thou art there."
Henceforth, those in Christ will still die in the sense of losing our bodies. But according both to His promise and to His demonstration, we shall receive them back, made perfect, immortal, and glorious.
John 11:25 Jesus said to her [Martha], "I am the resurrection and the life. He who believes in Me, though he were dead, he shall yet live."And meanwhile, from the moment we lose our mortal bodies until the Last Day and reunification with our incorruptible bodies, we shall never experience the darkness, the aloneness, the lovelessness, the hopelessness, the gradual draining away of our very soul and being. The Holy Spirit shall supply us His own Life, with fuller consciousness even than our finite bodies ever could before. In that sense, we shall never taste death.
John 11:26 "And whoever lives and believes in Me shall never die. Do you believe this?"
This is the difference it makes for us today and forevermore that Christ "descended into Hades".