an obstacle or hindrance; something that keeps one from attaining a goal
—Having a candy store next to my house is a stumbling block for staying on my diet.

In the Book of Romans and in 1 Corinthians, Paul writes that some Christians whose faith is weak believe it is wrong to eat certain kinds of food. Others, he says, who feel free to eat all kinds of food should not look down on those who restrict themselves, and those who can’t eat should not look down on those who can. He also warns the stronger Christians not to let their freedom be a “stumbling block” to weaker brothers. This would happen if weaker Christians are caused to sin because they do what they think is wrong after seeing other Christians doing the same thing:

Therefore, each of us will give an account of himself to God.

Therefore we must not pass judgment on one another, but rather determine never to place an obstacle [stumbling block] or a trap before a brother or sister. (Romans 14:12,13)

Now food will not bring us close to God. We are no worse if we do not eat and no better if we do. But be careful that this liberty of yours does not become a hindrance [stumbling block] to the weak. (1 Corinthians 8:8,9)

Originally, block meant “tree stump,” over which it is easy to trip.