Then he said to them, “How can they say that the Messiah is David’s son? For David himself says in the book of Psalms,
‘The Lord said to my Lord,
“Sit at my right hand,
until I make your enemies your footstool.”’
David thus calls him Lord; so how can he be his son?”
In the hearing of all the people he said to the disciples, “Beware of the scribes, who like to walk around in long robes, and love to be greeted with respect in the marketplaces, and to have the best seats in the synagogues and places of honor at banquets. They devour widows’ houses and for the sake of appearance say long prayers. They will receive the greater condemnation.”
This is the end of a debate Jesus had been having with the Pharisees, Sadducees, and Scribes. At the end of the last passage Jesus won a decided victory in which they acknowledged His teaching, and also became afraid to continue the argument. But Jesus, in this short passage, pressed the argument further by driving home His authority, which He knew they were still questioning.
Every Jew of that time KNEW the Messiah would be the son (or descendant) of David due to various passages in the Old Testament, mostly in Isaiah I think. But Jesus pointed to a Psalm that clearly indicates the divinity of the Messiah. Jesus, then, in this passage was claiming to be both. He was both man and God. Of course, we already know this from reading the first couple chapters of this Gospel. But the Pharisees had never heard such a thing. We can presume they were outraged, partly because they typically were outraged about anything Jesus said, and partly because this would be the fuel for the fire they would use to persecute Him.
But Jesus still wasn’t done. He made a very public, very abusive condemnation of the scribes. Why? Seriously, what was the point of a loving Messiah throwing down such a scathing insult? I imagine not so the people would “beware” of the scribes the way we say “beware of bears”, but so they would beware of becoming like them. So they would not be more concerted with how they looked than they were of taking care of others.
And this warning is still so relevant today! Imagine if the passage said: “Beware of those who go through town wearing expensive, designer clothes, who love being treated like an important person, and who like to be VIPs at church and society functions. They live by exploiting the poor, but make sure to post Bible verses on their facebook for everyone to see.” Things haven’t changed much in the last 2000 years.