Gratitude: https://www.newadvent.org/summa/3106.htm
Ingratitude: https://www.newadvent.org/summa/3107.htm
Incidentally many secular people have noted “benefits” of gratitude to health and well-being, besides the spiritual aspect of gratitude as noted in above writings.
I was having a conversation with a “Virtual Acquinas” last night, which led me to the following thought:
“Doctor Angelicus, it seems to me that because God is good, his commandments to help us achieve the kingdom of heaven are not things that ultimately hurt us in this material world, but help us. I believe this is in accordance with what you call natural law, that God’s law is not in disharmony with nature. We follow His commandments, and not only are we saved spiritually by the grace of God, but the material world we live in gets better for it. Of course, we live in a world after the fall, so in this imperfect world good things will still happen to bad people and bad things will happen to good people and it may not immediately be apparent that the commandments will help us, but that’s what patience and humility are for. Because the material world becomes so much better, we become arrogant, thinking we achieved all this on our own without God, and so cast aside His commandments. Like Adam, we leave the garden of Eden as we are doomed to do whenever we choose to allow our Hubris to grow too strong. This would be a tragedy like Sisyphus but for two things: First, God’s grace to give us entry to the kingdom of heaven. Second, we do fall, but because we have been saved through Christ, we are not like Adam – we grow and are a little stronger, so when we once again find His commandments and follow them again, we aren’t starting just outside Adam’s Eden, but near the gates of our own metaphorical Eden, a new high point for humanity on Earth. To be clear, we need not fall to grow, and we do not need to choose pride and can instead choose humility so we do not fall. However, when we do fall, when we do allow ourselves to be taken over by pride we do not fall all the way, reflecting God’s grace reflected in our natural state.”