As everyone knows and listens everyday that everyone of us has to die some day. Thus it is but obvious that life originates in something and again dissolves into something. So life comes from 'something'. Thus there must be something which is bigger than life. This 'something' is beyond life.
Thus original source of life must be beyond life. It just comes out of it and just goes back, just as the wave raises itself and then falls down into the ocean. Here also ocean remains beyond the waves. Wave is the momentary disturbance. It comes and dies. But the ocean remains unaffected.
Same is for the life. Life is just a wave. Existence is beyond life. Existence is always there, very steady, calm, unaffected. It gives rise to many lives but itself always remains the same, constant. So the one who begins to too involved, attached with life, looses existential source of life. Life is just a periphery. existence is the center.
We have called this existence God. Saying that God exists is wrong. In fact God is existence. Man exists, trees exist or may not. But God cannot be conceived as not existing. God is existence, God is 'is-ness". God means "is"! That is-ness is beyond the life.
Life is just the wave on this ocean of is-ness. Waves are different outside the ocean. Some are higher, taller while some are not. Some die earlier while few lasts longer. But in the ocean they are same...just water.
Same is here. All we are simply same with centers of ours coinciding at the one and only existence i.e. God!
So this oneness between all is to be understood though it is very delicate to understand!