What count among the saddest words in the New Testament? One scholar says Luke 6:46 is incredibly sad, when Jesus asks his disciples: "Why do you call me 'Lord, Lord, and do not do what I say?" Jesus has just talked about a "good man bringing good things out of the good stored up in his heart...for out of his heart his mouth speaks." That a person's character shows, and you can trust good words because they reveal a good heart. Character will out. And, then, Jesus has to reprimand some who have not acted seriously on the good things he has shared with them.
It's brutal reality that you can say Jesus' name, ernestly claim to believe him and follow him, but not actually do anything to prove it. Surface claims! Remember that old challenge: "If you were on trial for being a Christian, would there be enough evidence to convict you?" Talking, believing, feeling don't impress Jesus when there's no action. That's why the story of digging down to rock so appropriately follows (verses 47-49).
I am working on the implications of this question for a new sermon, this coming Sunday (for First Baptist Church, Downers Grove, Illinois). As always, any insights are welcome.