When you sin against your brothers, weak as they are, you are sinning against Christ. From chapters 8-14, Paul addresses the liturgical chaos that was playing openly in the Corinthian community. Chaos was being bred and nurtured in the intellectual disparity (knowledge) of the members, that is, between those who were knowledgeable and those who relied on others for direction. In the passage we have read today, the specific issue that Paul is addressing concerns the eating of meat offered to idols. The city of Corinth had not yet gotten rid of its gentile background (all indications pointed to this being almost an impossibility. As a busy port, Corinth was a melting point of many cultures). As a cultural crossroads, Corinth was also a religious melting pot: religions not only sprouted but also thrived in Corinth. As a consequence, Corinth, as were many other trade centers along the Aegean Sea, became home to many temples. And because the temple attendants could not keep pace with the amount of meat that was sacrificed on these temples on a daily basis, the temples became cheap-meat markets. Many of the residents frequented the temples to buy their meat for consumption at home. Upon the arrival of Christian faith, a conflict of conscience arose among those who became Christians: should they continue buying meat from the temples (the meat that was sacrificed to idols), or should they cease doing so? The knowledgeable members argued (rightly) that since the gods to whom such meat was sacrificed did not exist, there was no sin in consuming such meat. However, not all bought into their argument. Those among them who had weak conscience saw consuming such meat as participating in idolatry and as such was sinful. 
While Paul agreed with those who saw no sin in consuming meat sacrificed to idols, he nonetheless had beef with them for their total disregard of their weaker brothers and sisters: “ Not all have the knowledge that you do, and if you insist in acting according to what you know and in the process cause your brother/sister to sin, you are guilty of his/her sin.” It was the responsibility of the knowledgeable members to be on guard so as not to be the cause of their weaker brothers and sisters’ downfall. This is what belonging to the same body requires of a baptized individual: looking out for one’s brother/sister lest one commits the sin of Cain (who said he was not his brother’s keeper). Baptism calls an individual to be weak with those who are weak for the sake of the body of Christ (cf. Romans 15:1). 
The members whose consciences were strong had the obligation of minding about the faith of their brothers and sisters who could be easily scandalized. They needed to sacrifice their “rights” for the good and unity of the group. Their baptism had united not only to Jesus but also to one another. Consequently, what affected one was affecting all. The “stronger” members, by virtue of their knowledge, needed to have been aware of this.