what God is not like
Aquinas says the mystery behind it all is different than that.
God is not made of physical stuff like we are. God doesn't have
a beginning, God doesn't change, God doesn't perish; God doesn't
go through a series of life phases. Unlike us, God can all happen
God doesn't change
Space-time is obviously part of the fabric of the known universe.
So if we're thinking about the mysterious source of the universe,
it is reasonable to say that it is outside the space-time continuum.
And in our world, things change through time. So if one is outside
time, it is reasonable to deduce that one doesn't change. And
this is what Aquinas says. God doesn't have a beginning, a middle,
or an end because God is outside time, having created it.
God isn't a person
Each of us is made of stuff, existing as unique individuals within
our life forms. I am a person in the category "Human;"
Mr. Spock from Star Trek is an (imaginary) individual in the category
"Vulcan." And even though we have given God a name,
which implies personhood and individuality, Aquinas doesn't think
that God is a person; he is not an individual in the species
"God" that happens to have created the world.
God isn't dependent on the stuff of existence
Space, time, matter, the stuff of life: God isn't like, doesn't
have, and isn't dependent upon any of it. If Aquinas were alive
today, he would probably say that God exists apart and different
from everything we know to be associated with space, time,
and matter, which I guess is a reasonable deduction since we
consider that all to be a part of the physical universe whose
cause we're trying to describe.