Why Was Jesus Called 'The Son of David?'

Because Jesus Christ is the most influential person in human history, it's no surprise that His name has become ubiquitous throughout the centuries. In cultures all over the world, people know who Jesus is and have been changed by what He has done.
48 Many rebuked him and told him to be quiet, but he shouted all the more, “Son of David, have mercy on me!”
There are several other examples of people using this language in reference to Jesus. Which begs the question: Why did they do so?

An Important Ancestor

The simplistic answer is that King David—one of the most important people in Jewish history—was one of Jesus' ancestors. The Scriptures make that clear in Jesus' genealogy in the first chapter of Matthew (see v. 6). In this way, the term "Son of David" simply meant that Jesus was a descendant of David's royal line.
This was a common way of speaking in the ancient world. In fact, we can see similar language used to describe Joseph, who was Jesus' earthly father:
Neither Joseph nor Jesus was a literal child of David. But again, using the terms "son" and "daughter" to show an ancestral connection was common practice in that day.
Still, there is a difference between the angel's use of the term "son of David" to describe Joseph and the blind man's use of the term "Son of David" to describe Jesus. Specifically, the blind man's description was a title, which is why the "Son" is capitalized in our modern translations.

A Title for the Messiah

In Jesus' day, the term "Son of David" was a title for the Messiah—the long-awaited Righteous King who would once and for all secure victory for God's people. And the reason for this term has everything to do with David himself.
Specifically, God promised David that one of his descendants would be the Messiah who would reign forever as head of God's kingdom:
“‘The Lord declares to you that the Lord himself will establish a house for you: 12 When your days are over and you rest with your ancestors, I will raise up your offspring to succeed you, your own flesh and blood, and I will establish his kingdom. 13 He is the one who will build a house for my Name, and I will establish the throne of his kingdom forever. 14 I will be his father, and he will be my son. When he does wrong, I will punish him with a rod wielded by men, with floggings inflicted by human hands. 15 But my love will never be taken away from him, as I took it away from Saul, whom I removed from before you. 16 Your house and your kingdom will endure forever before me; your throne will be established forever.’”
Other Messianic prophecies in the Old Testament made it clear that the Messiah would heal the sick, help the blind to see, and make the lame walk. Therefore, the term "Son of David" had a specific connection to the miracle of healing.
We can see that connection at work in this incident from the early portion of Jesus' public ministry:
22 Then they brought him a demon-possessed man who was blind and mute, and Jesus healed him, so that he could both talk and see. 23 All the people were astonished and said, “Could this be the Son of David?”
Matthew 12:22-23 (emphasis added)
The rest of the Gospels, along with the New Testament as a whole, seek to show the answer to that question was a definitive, "