Excellent question @LKHHKL!
Throughout the ancient world, worshippers of Greek and Roman gods (and others) would sacrifice their animal offerings in the temple of Zeus, Diana, Mars, etc. They would hand their goat or pig or chicken to the priest who would burn it on the altar. The worshipper would eat a portion (identifying himself with the sacrifice), the priest would eat a portion, and the rest would be given to the god or goddess.
But what exactly did the god or goddess do with the rest of the meat? I Corinthians 10:25 explains that it was sold in the shambles, or the meat market which was the temple’s butcher shop. It was a source of revenue for the temple. Obviously the priests could not consume all of the steady stream of sacrifices that came through their temple day after day, so they had a butcher’s outlet right there by the temple where it was sold to the public.
Now consider that the animals offered to a god had to be the very best of one’s stock. Consider also that the priest had no overhead to cover - he got the meat for free from Zeus’ worshippers. So everyone in town knew that the very best meat for the very best price was sold in the temple outlet. So that was where virtually everyone bought their meat. No brainer!
But virtually everyone did not include one very important group - the Jews!
They would go to a Jewish butcher not associated with any pagan temple to buy their meat even if it wasn’t as high a quality or as low a price as the meat that had been sacrificed to an idol for one reason - they considered anything sacrificed to an idol to be polluted - jinxed - the most non-kosher of all non-kosher foods possible!
So now here are Gentiles who’ve worshipped Apollo all their lives, and gotten good deals on their meat in the temple market. Now they’ve turned to Christ for salvation. But Christians don’t have kosher diets (Colossians 2:16-17). So it never crosses their minds to go anywhere else to buy their meat than where they’ve always gone.
Until they try witnessing to their Jewish neighbors with a Zeus-kabob in their hand. Or they invite their Jewish friends over for lamb burgers. And an awkward moment comes when a conscientious Jew asks, “Um, where did you say you bought this mutton at?”
So James is writing to these Gentile converts and asking them to avoid eating meat sacrificed to idols out of respect to their Jewish neighbors that they’re trying to win to Christ.
The issue is, would you be willing to sacrifice some things that you know aren’t really wrong in themselves in order to remove a barrier, an offence, that might undermine your testimony in the eyes of those around you?
We don’t really have Zeus temples in our culture, but can you think of any parallels in our day? Something that people in the world might see you do or hear you say or a place they might watch you enter that would make them question the sincerity of your faith?