what is good?

I hate how I am so busy in design, yet when I find moments where I
don't have much to do I have no idea what to do with myself. Yesterday
I took a bath and read Thomas Aquinas. His thinking is amazing and I
have to keep rereading to really understand what he is saying. He says
that "everything is good through its own essence" (Summa theologiae,
Part I On the Goodness of God). I'm not quite sure what this means. I
always thought everything was good through the essence of God. But if
God alone is essentially good, and we all come from God, then perhaps
this is true that everything is good through its own essence because
our essence comes from God? It does go on to say "Although any thing is
good insofar as it has existence, still the essence of the created
thing is not its existence, and therefore it does not follow that the
created thing is good in its essence."

And when we think about
good most things are not good in of themselves. Things are good because
they get us things which make us happy. Money wouldn't be good if it
wasn't able to buy things. Food wouldn't be good if it didn't give us
energy. So how do we call ourselves good when people assume they are a
good person? Are we "good" people because it gets us something? Or
really is it that we are not essentially good, but there is a creator
who is ultimately good in Himself? But is this really how God is? Don't
we view God as giving us freedom of sin, spending eternity in Heaven.
Believing in God has incentives as well. So is there anything which is
good that is good in itself? Is Aristotle right in saying happiness is
the only intrinsic good that is also not extrinsic? That happiness is
the highest good? As a Christ follower I would argue Christ is the
highest good. That yes, happiness does seem to be an end in itself, but
it is also not constant. It comes and goes. Christ is always.