This is true even when the thing that I did was allowable and my conscience was clear to do it. For instance, I may have a clear conscience before the Lord that it is ok for me to have a drink of alcohol from time to time. But if my drinking alcohol causes my brother to be tempted to use alcohol in a sinful way, then I have in fact caused my brother to stumble and thus have sinned against Christ.
I cannot live in a vacuum as if I am the center of the universe, because what I do affects others. What I do can either build others up or tear them down. It can benefit my brother or it can break him. Therefore, I must not only live for God and myself, but also for my brother. Jesus told us that the greatest commandment is to love God. Then he told us that the second is like the first – love your brother.
Lord, show me those things that I should lay down for my brother and give me the grace to do it.
9 But take care that this right of yours does not somehow become a stumbling block to the weak. 10 For if anyone sees you who have knowledge eating in an idol's temple, will he not be encouraged, if his conscience is weak, to eat food offered to idols? 11 And so by your knowledge this weak person is destroyed, the brother for whom Christ died. 12 Thus, sinning against your brothers and wounding their conscience when it is weak, you sin against Christ. 13 Therefore, if food makes my brother stumble, I will never eat meat, lest I make my brother stumble.– 1 Corinthians 8:9-13