In fencing, the riposte is an offensive action taken just after parrying a blow from one's opponent. Sociological experts of the ancient world talk about the common debates of the time being one of "Challenge-Riposte"; in other words, a person is challenged in the debate and must defend against the charges, but then are given a chance to response (riposte), often in a witty retort.
Well Jesus has just spent all day being challenged and defending Himself well. It is time for the riposte. And He throws back two challenges to the Jews, the first of which we will discuss this week.
"Now while the Pharisees were gathered together, Jesus asked them a question, saying, 'What do you think about the Christ? Whose son is he?' They said to him, 'The son of David.' He said to them, 'How is it then that David, in the Spirit, calls him Lord, saying, 'The Lord said to my Lord, sit at my right hand, until I put your enemies under your feet'? If then David calls him Lord, how is he his son?' And no one was able to answer Him a word, nor from that day did anyone dare to ask Him any more questions." (Matt 22:41-46)
Here, Jesus completes His win of the debate by challenging the Pharisess to something that they are afraid to answer. His trap is perfect, too.
He asks them to identify the Christ, and they properly answer that the Christ is prophesied to be the son of David (2 Sam 7:14-16). Yet also, Jesus points out that David calls the Christ in prophesy as his Lord, indicating that he will be of higher authority than David is.
Now the Pharisees are starting to see that trap into which they have fallen. They have heard the people calling Jesus the Son of David (Matt 15:22; Matt 20:30; Matt 21:15)--indeed, this is one of the reasons that they chose to try and fight Him.
But now Jesus has put them in a tough spot, because Jesus is saying that the son of David is David's Lord. Recall that most Jews thought the Christ/Messiah would be a new king of Israel, but Jesus is claiming that the Christ is greater than David. This means that He is at least saying that the Christ is more than just a king, and possibly claiming that the Christ is actually equivalent with God.
So Jesus has put them in a rough spot. They cannot deny that the son of David is the Christ. Now He has pointed out that the son of David is greater than the King of Israel; if they agree, then they are giving their tacit approval to the throngs who believe in Jesus as Christ that He speaks for God! Thus they simply feign ignorance, and agree amongst themselves that they will stop trying to challenge Jesus openly. They realize now that to bring Him down will require subtly and working from the shadows, for they do not like the way He is now going with the conversation.