Human beings from the beginning of his existence had to believe firmly that this human life is a transitory phase. Otherwise this life starting with birth and ending with death had no other meaning or purpose for him if he did not believe that there is a level of existence higher than his own existence.He believed that that state is permanent and eternal and this in different faiths have been stated as reaching heaven,attaining nirvana, moksha,liberation whatever it is.
There is a very beautiful illustration of two birds ,first told centuries ago and being told again and again after that ,explains the journey of an individual towards truth.
There were two birds on a tree on 2 different branches,one higher and one lower.The bird on the higher branch was very peaceful and calm and was in absolute bliss. The bird on the lower branch was very restless and always busy eating fruits from the branch, worrying for food ,survival, sometimes happy ,sometimes in sorrow .
Once in a while it would look upon the bird on the higher branch and would wonder how that bird was so blissful and makes an attempt to find out why it was so happy ,fly one branch higher ,to reach the bird on the highest branch , but when it reaches the higher branch it gets busy again eating the fruits of that branch until it eats a sour fruit , gets restless again and looks upon the higher bird again make another step towards the bird until finally the bird reaches the highest branch and to its surprise finds out that it has merged into the bird there and becomes blissful like the bird there.This story has a very deep inner meaning of human existence and its journey towards the truth(God)The lower bird is compared to our present level of existence at the human level ,we are always busy with this life that we don't tend to look for some higher meaning or truth for this life until we have a bad sour experience ,its then we want to look towards some higher truth or meaning.
Whatever the truth represented by the higher bird is, it helps and gives hope to human beings that there is something permanent beyond death.