The separation was never a mistake.  It was a lie we told ourselves for a purpose.  The purpose being the desire to create, to give, something new.  Something that had not yet been known.  Something other than all the experiences of God.  God is all and God is love.  He wants more to love, more to know, but we can’t know more when we are in perfect unity.  We could never encounter ourselves, see ourselves, as we do in separation.  We know what we are by seeing what we are not.  And this is the purpose of the illusion of separation.  Chaos is our teacher and order is our home.