This is a very brief condensation of a parable that Matthew recorded more fully. Matthew's interest in it connects with the mention of false teachers that occurs in the context of his account of the sermon. Luke simply lifted the main point of the teaching out and inserted it in his account. His interest was primarily Jesus' warning to disciples to apply His teaching to their lives. Profession of discipleship is one thing, but what identifies a true disciple of Jesus is really doing God's will (cf. James 1:22-25).
A disciple cannot legitimately refer to Jesus as his or her lord and ignore what He teaches. The double title was common in Judaism to strengthen the form of the address (cf. Gen. 22:11; 46:2; Exod. 3:4; 1 Sam. 3:10). Here it implies great honor. "Lord"was a respectful address, as we have noted, but in view of who Jesus was it came to imply the highest respect. Used intelligently it implied deity, messiahship, and sovereignty. However everyone who used this title, even Jesus' disciples, did not always imply all of this when they used it, especially before Jesus' resurrection and ascension.
