The goodness of God is seen everywhere, and in everything, but it is particularly evident in the gift of food. One of our customs is to “say grace” every time we partake of a meal, and this is actually a very sound tradition. The Bible doesn’t command it anywhere, but it is truly a devout reflex that does not want any opportunity to thank God for food to pass by us.
That being the case for ordinary food, how much more should we thank God for this food. In the first place, it is a Eucharistic meal, and the word eucharist means thanksgiving. How could we partake of the very food of thanksgiving without being eager to give thanks?
Secondly, God has given us this food to strengthen us for our walk with Him, and so this supplies you with the grace to enjoy everything else in your life rightly. And so, if you are thankful for your marriage, your job, your home, your children, it is here that you continue to receive the grace of thanksgiving to continue your thanksgiving. Saying thank you takes something, and God gives you what you need in order to be able to do it.
Third, Jesus Christ did not die for you on this table—He died outside Jerusalem, outside the camp, two thousand years ago. This table is a memorial of that sacrifice, a memorial not only for us, but also for God. Just as the rainbow reminds God not to flood the earth again, so this Table reminds Him not to hold your sins against you. Do not allow your grasp of certain theological truths get in the way of this. Of course, God does not need any reminders—He knows everything. And this is yet another reason to be thankful. He stoops in yet another way, and gives to us the great privilege of reminding Him that we are a forgiven people.
This is all tied in with the mystery of creation, and the nature of the Creator/creature divide, for which we are also thankful.