'Consciences' in the Bible

However, not all [believers] have this knowledge. But some, being accustomed [throughout their lives] to [thinking of] the idol until now [as real and living], still eat food as if it were sacrificed to an idol; and because their conscience is weak, it is defiled (guilty, ashamed).

When you sin against your brothers in this way and wound their weak consciences, you are sinning against the Messiah.