Now such like words or deeds wherein nothing further is sought than the soul's delight, are called playful or humorous. Hence it is necessary at times to make use of them, in order to give rest, as it were, to the soul.
It seems as though Thomas believes that there is a positive impact that can be taken away from divulging in games, and that has to mainly do with the soul. He tends to weave in different ideas in religious texts and words of people who contain lots of wisdom to form this idea that the soul of an individual needs to find delight in these kinds of games. He is essentially saying that words such as playful and humorous were invented so that individuals could discover different ways to create such strong or positive emotions that come from different activities. If playing some kind of medieval game creates "humor" or inspires "joy" in someone's heart, then it was a game that was meant to exist and be played by all.