What does Mark 10:47 mean?

In Hebrew, Jesus' name—Yeshua—was common. Not many people of that era were referred to with family names. Rather, they were often differentiated by what they did, like Simon the tanner (Acts 9:43), or where they are from, like Mary Magdalene (Mark 15:40). Despite what some mistakenly assume, Jesus' last name is not "Christ." He didn't have a family or "last" name. Bartimaeus knows that this is "the" Jesus when he hears that this is the one from Nazareth.

Jesus is obviously not David's literal son, as David lived a thousand years before. "Son of David" refers to the promise God made David that the king would have an heir who would reign over Israel forever (2 Samuel 7:12–16); God also promised to "raise up for David a righteous Branch," the Messiah, who will rescue Israel from her enemies (Jeremiah 23:5–6). Jesus is descended from David on both His mother Mary's side (Luke 3:23–38) and His adopted father Joseph's side (Matthew 1:1–16).

On previous occasions, when Jesus is identified as the Son of God or the Messiah, He tells the speakers to stay quiet (Mark 1:24–25; 3:11–12; 8:29–30). With Bartimaeus, He does not. We don't know if Bartimaeus really thinks Jesus is the Messiah or if he's trying to get Jesus' attention with such an honorific. It is interesting to note that directly after Bartimaeus calls Jesus the Son of David, Jesus is welcomed in Jerusalem like a king (Mark 11:1–10).

"Mercy" is from the Greek root word eleeō and means "to give aid to something that is in need." Bartimaeus exemplifies the meaning of "poor in spirit" (Matthew 5:3). He knows there is nothing about him that warrants Jesus' attention. He has faith that Jesus' favor is not something he can or must earn. He just needs to ask.