Paul is dealing here with false teachers. He had earlier addressed their false doctrines. In this passage, he is concerned with some of the practices they advocated, including abstaining from marriage and certain foods.
Why they advocated abstaining from some foods and what those foods might be is unknown. They could have been promoting Jewish dietary laws, forbidding eating meat that had been sacrificed to idols, or some other unknown position.
But Paul is clear in his rebuttal of their teaching. Everything God created is good (Gen. 1:31). So all food can be received and eaten with thanksgiving.
Of course, some foods are healthier than others. And overeating can be a problem. But there should be no “religious” reason to abstain from any food.
I grew up in a home where giving thanks for our food occurred before every meal. And that is a practice I have continued in my own life.
It is a prayer of thanksgiving for the food and seeking God’s blessing on the meal. And Paul tells us here that this prayer of thanksgiving sanctifies the food. It makes it holy.
My sanctified food does not somehow change. It is still the same food. But when I eat that holy food, it is as though God is at the table with me, partaking of the meal with me. And that makes it special.
So, as you take your meals each day, don’t forget to offer a prayer of thanksgiving and blessing for your food. And then rejoice in God’s presence at the table with you.