Most of us are familiar with the Greek philosopher Plato.  Not as many of us, I suspect know the details of the way he saw truth.  Plato said that truth, that is, truth as Truth, though it can be found in this world, is not grounded in this world.  If we wish to find Truth in this life, we must look beyond the world, look to a world of eternal "Forms" from which we ultimately derive all knowledge about this world.  Though we can experience Truth in this world, we can only do so if we look for it through the lens of its world, the world of eternal Forms.
     What's Plato's proof of this eternal and invisible world?  When we distill it down to its particulars, we see that it is very similar to the proofs that many of us use to affirm the existence of God today.  In sum, Plato argued (and this was many centuries before Jesus appeared on earth) that so long as we live in this world, we cannot really understand all of it.  Why?  Because we are part of it.  We need to be able to step outside of this world to really know what it is and what it means.  Hence, the world of Forms.  It's like being in a box (Plato used the analogy of a cave).  If we are in a box, all we can see is the inside of it.  We do not know what the box looks like and we do not know where the box is.  All we know are its four walls.  The walls of our finite world.
     Of course, we do not need to believe in a world of eternal Forms.  Nor do we necessarily need to believe in God.  Either way, we may well have a satisfactory life.  However, we may be missing a much bigger point:  do we really want to live and die without ever knowing, honestly, why we were ever here?