Picture two skydivers. They are both free-falling. Their speed is the same. They both seem to be free. They are not entangled in any cords. They are not restrained by any safety wires. They are as free as birds – it seems. But there is one crucial difference: only one of them has a parachute.
Does this change the sense of freedom that they enjoy? Yes. Both are free to full with gravity, but only one of them is free not to. The other is a slave to gravity, and gravity will kill him in the end. If he can somehow deny that he has no parachute he might be able to have an exhilarating experience. But if he realizes he is doomed he will be enslaved through fear during his entire fall, and all the joy of this so-called freedom will vanish. He must either deny the reality (which will mean slavery to illusion), or succumb to fear (which will mean slavery to terror), or be rescued by someone with a parachute.
So it is in this world. Apart from Christ, we are subject to slavery all our lives through fear of death. – John Piper, Future Grace