Meditation is like unto the water of a pond--made murky by agitation--being calmed so as to allow all the mud and silt to settle to the bottom so that the water becomes clear, and you can see all the way to the bottom.
And then you will discover there is something at the bottom of your mind that can only be seen when your mind is completely calm. Something deeper than the root of your thoughts; below the foundation of your personality.
And it is the same thing that is at the bottom of the so called physical world; deeper than the root of all matter; below the foundation of the universe.
It is eternal; it is the real you, and that is why and how you are immortal.