In Mark 7:18, Jesus states, “Are you still so dull?” He asked. “Do you not understand? Nothing that enters a man from the outside can defile him, because it does not enter his heart, but it goes into the stomach and then is eliminated.” So why do Catholics give up meat?
Some believe that abstaining from meat during Lent was a way to give up luxury, especially during ancient times. Further, humans are considered warm-blooded animals, so Catholics only ate cold-blooded animals such as fish on Fridays during Lent. However, abstaining from consuming meat during this obligatory Sacred Tradition also has ties to fish sales.
According to NPR, “But fish—well, they’d been associated with sacred holidays even in pre-Christian times. And as the number of meatless days piled up on the medieval Christian calendar—not just Fridays but Wednesdays and Saturdays, Advent and Lent, and other holy days—the hunger for fish grew. Indeed, fish fasting days became central to the growth of the global fishing industry.”