It is reasonable to have gratitude. It is loving to have thankfulness.
"When you feel gratitude, you're pleased by what someone did for you and also pleased by the results." --vocabulary.com
Gratitude is recognized and expressed by the intellect. Thankfulness is a spiritual posture and way of being in the world.
gratitude to God
This is a specific application of gratitude that is beyond the intellect, having surrendered linear causation, i.e. "God works in mysterious ways" (the saying is at 530).