Zacchaeus may be most recognized as the guy who climbed up a sycamore tree--but there's much more to his character. He was a chief tax collector and likely very unpopular among the people of his day. Ironically, he was also a man of "short stature", which didn't make him very intimidating despite his lofty status as tax collector; perhaps it even made him insecure. Perhaps he clung tightly to his status and achievements as a tax collector in order to feel some sense of worth, though inwardly he grappled with the frustration that he could never fully measure up, that he had to continue to put up a mask in order to appear better than he really was. Still, he climbs up the tree to see over the crowds that surrounded Jesus in an unexpected demonstration of spiritual hunger and curiosity. Jesus, noticing this, seeks Zacchaeus above the crowd and personally calls him out by name: “Zacchaeus, hurry and come down, for I must stay at your house today" (Luke 19:5). This must have been such a shock for Zacchaeus--that he would be noticed by Jesus.
Though Luke 19 doesn't record details of the conversation between Zacchaeus and Jesus in his house, it is clear that, after meeting Jesus, a 360 degree turn happens in Zacchaeus' life. He goes from a man who clung to his money to a man who is able to say, "Behold, Lord, the half of my goods I give to the poor. And if I have defrauded anyone of anything, I restore it fourfold” (Luke 19:8).
Jesus calls him a son, calls him saved, simply because Zacchaeus was willing to seek after Jesus and relate to him as a sinner. Given his new identity, Zacchaeus is set free to love people; the taker becomes a giver, the lost becomes found. The crowds around Jesus, on the other hand, "grumbled" at all of this, saying amongst themselves, “He has gone in to be the guest of a man who is a sinner” (Luke 19:7). Unable to recognize their own sinfulness, the crowd is unable to make a personal connection with Jesus like Zacchaeus has. Jesus says that he has come to connect to and save people like Zacchaeus--people who are willing to recognize their lostness: "For the Son of Man came to seek and to save the lost" (Luke 19:10).