People liked tax collectors back then just about as much as they do now. Which is not much.
In fact, it was even worse if you think about it. Most of the time we dislike the Internal Revenue Service because they take our money. That's generally enough for most people. But Zacchaeus is going to be even more disliked than the modern IRS agent. For one, he represents the Romans, who are collecting the taxes. Most Judeans hated the Romans, who had walked in, made themselves comfortable and started helping themselves to the pantry without even wiping their feet first. The tax collectors took their money under the threat of Roman force, so their presence was an unhappy reminder to the Judeans that they were a conquered people.
For another, as we will later learn, Zacchaeus adds to his unpopularity by taking not simply what he's supposed to take to make his payments to the Romans, but he cheats people too and takes far more than people owe. The Romans didn't particularly care about this as long as the taxes got paid and people didn't riot or anything. As long as Zacchaeus made his payments, he could be shaking everyone down for every last red cent they had and the only thing the governor might do is shrug or "suggest" he should get cut in on the action.
So when the word gets around that Jesus, the well-known traveling teacher, healer and worker of miracles, will be coming through town, people line up to see him. Zacchaeus is as curious as the next fellow and wants to see him as well, but he's too short to see over the people lining the road. Now, most of us have watched parades or other public events that people line up to see. When people bring their children, who as a rule are short and can't see and prone to gripe about it, most folks will stand aside a little to let the children be in front. Since we can see over them, it's no skin off our nose, although we might need to be ready to grab them from harm's way when those crazed clowns start driving their little cars all over the place.
No one does this for Zacchaeus, though, do they? I suspect many stayed right where they were and may have even shifted position slightly in order to keep blocking his vision. Maybe someone even said, "Why don't you stand on your money?" or asked him why his friends the Romans didn't help him see Jesus. We don't know that for certain, but I don't know how many people, when faced with the chance to get a little of their own back from a disliked individual, pass it up. So Zacchaeus just climbs a sycamore tree to see the hubbub as it happens.
And Jesus notices him there and says, "Zacchaeus, come on down! You're the next contestant on 'Get Your Life Right!'" OK, not exactly. But what he does do is invite himself to dinner at Zacchaeus's house. I imagine not many people did that -- either invite themselves to his house or even show up there of their own free will, since Zacchaeus was a hated tax collector. And sure enough, people grumble about Jesus's choice to do so. Zacchaeus is a sinner, after all, and here is a teacher of the Law, one who knows that Law as well as the Prophets and all the scriptures, and he's ready to be the guest of someone who cheats the innocent and basically steals from people using Roman force.
We have no idea what they talked about during dinner. Maybe Zacchaeus and Matthew swapped tax collector stories. Maybe Jesus or another disciple talked about some of the things that had happened during their travels. But at some point, Zacchaeus felt the need to change who he was. So he made a bold declaration: "I will give half of everything I have to the poor and I will pay back four times the amount I defrauded from everyone I overcharged."
Jesus is pleased. "Today salvation has come to this house!" he said. Jesus knows human nature. He knows how easy it would be for Zacchaeus, surrounded by the well-known teacher and his followers, to say things like, "Well, I'll be a changed man from now on, yessirree!" Or, "You've certainly given me a lot to think about, Rabbi." Or maybe even, "I'm going to see what I can do with my influence with the governor to see about the Romans having a more just tax policy."
Nothing like that. Just a very specific set of actions, a detailed outline of what will be a radically changed life. And Jesus knows that such a change comes when a life disconnected from God becomes a life connected to God, so he notes that with his comment. It's kind of an odd way for Jesus to phrase things. After all, he's salvation, isn't he? In one sense, salvation came to Zacchaeus's house when Jesus showed up. But Jesus doesn't proclaim that salvation as the reality of Zacchaeus's life until after Zacchaeus commits to changing his life.
Jesus shows up in our lives on a regular basis, and we don't much more say in how that happens than Zacchaeus did. So salvation has come to us all. But we have to decide, also as Zacchaeus did, whether or not salvation comes to us for real or just has a cup of coffee and is on its way. I don't know if people treated Zacchaeus differently or not after he changed like this. I'd like to think so, but we all know folks who don't allow for the possibility that people can change or who like their grudges more than they like people straightening out their lives. But I do know that anybody who knew him before Jesus met him had to be able to see the difference, now that "salvation had come" to his house.
Can those who know us see a difference? Do we look different from our "pre-salvation" selves, or at least different from the world around us? The answer will speak more than any sermon ever could about the power, love and grace of Christ.