Thus, sinning against your brothers and wounding their conscience when it is weak, you sin against Christ.--1 Corinthians 8:12 (ESV)
In a chapel address at the Master's College, Mark Dever made the following statement: "Christ so identifies with His Church, that how you treat each other as Christians is the way you treat Christ." Now that is a convicting truth! Paul clearly states in 1 Corinthians 12:27 that "Now you are the body of Christ and individually members of it." In 6:17, he wrote "But he who is joined to the Lord becomes one with Him in spirit." Therefore, when we sin against our brothers, who are members of Christ, we sin against Christ. Gossiping about our brothers, lying to our sisters, or weakening the consciences of our fellow church members are ways in which we can sin against our very Savior.
No other truth in the Bible can give us such love for our brothers and sisters as this: They are part of Christ. We should give fellow Christians the love due to Christ. Anything short of this (admittedly rather high) mark offends Christ and sins against Him.