Since the Fall of man people have been disclaiming responsibility for others. It was Cain’s excuse after he murdered his brother: “Am I my brother’s keeper?” (Genesis 4:9) But in Christ, we have no more excuses. We have to answer “yes” to Cain’s question; we have become our brother’s and sister’s keepers. What they do very much matters to us because Christ has reversed the curse of Cain – where Cain sought to separate himself from his biological family, Christ has bound us together into a spiritual family; the people with whom we will spend eternity.
Since we’re responsible for one another we’re called to help each other out. The goal is to get to what Jesus describes in verses 19-20: “When two or three are gathered in my name…” It’s in that gathering that the Father promises to answer our prayers and Jesus promises his presence among us. So James instructs us to “confess your sins to one another “ (James 5:16), and that “if anyone among you wanders from the truth and someone brings him back, let him know that whoever brings back a sinner from his wandering will save his soul from death and will cover a multitude of sins.” (James 5:19-20; cf. Galatians 6:1)
Jesus’s family matters to us, and we’re stronger and closer to Jesus together. So whenever someone is threatened by sin, we’re there to help one another in love.