Why does a weak believer get shaken when a mature Christian eats meat offered to idols?
The weak believer is still relatively young and weak in faith, so seeing a mature Christian eat meat previously offered to idols shakes him and becomes a stumbling block. Paul therefore says the mature believer should refrain from eating for that weaker believer’s sake, rather than use his liberty and cause problems.
Les explains that meat sold in the market often came from animals first offered in a pagan temple, and even a friend’s wedding feast might have been blessed by a pagan priest. The mature Christian understood that eating such meat did not commend him to God: whether he ate or not, he was neither better nor worse, and Scripture never forbids eating meat. But Paul warns that this liberty must not become a stumbling block to the weak. A mature believer can do these things and knows it will not hurt him, while the young believer, still relatively weak, gets all shook up by seeing what the mature fellow is doing. So Paul says that rather than cause problems in the life of this new believer, the mature believer should not eat the meat—do it for the weak believer’s sake.
But take heed lest by any means this liberty of yours become a stumblingblock to them that are weak.