SynopsisThis passage begins with the disciples coming to Jesus to ask him who the greatest in the kingdom of heaven is. As usual, Jesus’ answer probably surprises them: he calls over a child and has him stand in the midst of the disciples, and tells them that they can’t even enter the kingdom of heaven unless they become as humble as a child.
Jesus then takes a bit of a tangent, and tells the disciples that anyone who receives “one such child” in his name receives him (verse 5 (ESV)). More than this, but we should be careful never to cause any child who believes in Jesus to sin—if we do, it would be better to have a millstone fastened around our necks and be drowned in the sea. (A “millstone” is a large stone which was used for grinding grain; the point is that it’s very big and heavy. This would be comparable to us talking about giving someone “cement shoes” and throwing them into water.) Jesus doesn’t say better than what; the implication is that it would be better than dealing with his wrath.
ThoughtsThe first thing to notice about this passage is that Jesus doesn’t actually answer the disciples’ question. They ask who is the greatest, and instead he tells them that they can’t even get into heaven unless they humble themselves like a child. He doesn’t proceed to tell them that the more like a child they are the greater they will be, or talk at all about being “more” or “less” great—he simply tells them that they have to be humble in order to get into heaven at all.
Why is humility so important? Why do we have to be humble in order to get into heaven? Because we can’t do it on our own! There is nothing I can do to earn my way into heaven; there is nothing I can do for God that will make entrance into the kingdom of heaven my “right”. I have to rely on the work He has done, on my behalf. I have to admit (to myself and to Him) that I don’t deserve what He has done for me—and ask Him for it anyway. That takes humility. Not to mention the fact that I also have to compare myself with my God; to measure myself up against Him. If anything will make me humble, that will!
I don’t think Jesus’ tangent is specifically about causing children to sin; since he’s just said that we all have to be humble like children in order to get into the kingdom of heaven, I think he’s talking about causing any believer to sin. It would be better to be drowned in the sea than to cause a Christian to sin. Not that we can cause anyone—adult or child—to sin, they choose to sin on their own; but if the temptation to do so comes from us, woe be to us, because God will not be happy with us.