Matthew 12:23 All the people were astonished and said, “Could this be the Son of David?”
A miracle had occurred! The people were greatly surprised, impressed and amazed. I mean a man who was both blind and mute due to demon-possession was instantly healed. This is not a daily occurrence and the person who made this happen was obviously special – Jesus. It is also obvious that this person was holy and was from God, otherwise He would not fight against the kingdom of satan by expelling demons from people. Actually this is what Jesus told the Pharisees when they said that he got His powers from satan.
Mark 3:23-24 So Jesus called them together and began to speak to them in parables: “How can Satan drive out Satan? If a kingdom is divided against itself, it cannot stand.
The people also wondered if this man who had supernatural powers was the Son of David. They knew about the old testament prophecies of the coming Messiah who would be in David’s lineage.
Isaiah 11:1 And there shall come forth a rod out of the stem of Jesse, and a Branch shall grow out of his roots
Isaiah 9:6-7 For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. The zeal of the Lord of hosts will perform this.
God had promised David that his kingdom would never come to an end and this was fulfilled by the birth of Jesus the Messiah as a descendant of David who was the son of Jesse.
2 Samuel 7:16 Your house and your kingdom will endure forever before me; your throne will be established forever.
So the people were right to wonder if Jesus was the Son of David. Remember that in those days there were no printed Bibles and info was shared mostly by Word of mouth. How much more should we believe in God now that we have His Word in many forms including print and electronic?