Mark 9:42 continues Jesus’ teaching on the importance of receiving His people and treating them properly. We have seen in verses 36–37 that Christians must not show favoritism but must accept even those of lowly social status who love and serve Christ. Verses 38–40 warn us about having an approach to Christian service that is too exclusionary, that draws lines between believers where they should not be drawn and rejects as brothers and sisters in Christ those who are not part of our particular group even though they follow the Jesus of Scripture. Jesus then follows those admonitions with a reminder that He will reward all those who treat His people well and help meet their needs (v. 41).
Our Savior makes a related point in Mark 9:42, where He warns us about causing “one of these little ones” who believe in Him to sin. The Lord refers not merely to young children who follow Him; “little ones” signifies all believers. Though we grow into maturity as we follow Christ, we remain those who receive Him like a child—from first to last, we cast ourselves absolutely into His care, just as little children wholly depend on their parents for their lives (Matt. 18:1–4).
We can commit no greater evil against another believer than causing them to sin. After all, we impede their growth into Christlikeness and negatively affect their heavenly reward when we lead other Christians astray. So, it follows that treating other Christians properly entails doing what we can to avoid causing them to stumble. The end that awaits those who cause others to sin is horrible indeed. It is so awful that it is better for the person who leads others into transgression to have a “great millstone” hung around his neck and to be hurled in the sea. In the ancient world, a millstone was a stone placed on top of another stone and turned in order to crush grain into flour. The millstone was so heavy that it took several animals to turn it. To be thrown into the sea with a millstone around one’s neck would be certain death. The terror of this image would have been particularly real to Jesus’ original first-century Jewish hearers, for ancient Jews feared the sea, making death by drowning a particularly horrific end.
This warning applies to all believers, but it is particularly pertinent for teachers in the church because of their influence. Ministers, elders, deacons, Bible study leaders, and Sunday school teachers must all be careful what they teach lest they lead others astray.