Who am I?

I was there in the beginning
and I will be there at the end.
I am present throughout time and space,
and to the ends of the Earth.
I exist in other parts of the universe;
also in heaven and in hell,
inside and outside,
and within everybody.
I am in your home,
although not among the doors and windows,
and I am particular
about the rooms I inhabit.
You cannot see me
and many people do not know of me,
but I exist inside their heart.
Who am I?