He was a little man with a big problem. Jesus was coming to town but the crowds kept Zacchaeus, who was a short man, from seeing him. A familiar Sunday school song tells the story:

Zacchaeus was a wee little man
And a wee little man was he.
He climbed up in a sycamore tree
For the Lord he wanted to see.

As the chief tax collector of Jericho, he was not a popular man. Since he had cheated many people, he had many enemies. So climbing up in a sycamore tree was both ingenious and prudent. The same Sunday school song explains what happened next:

And as the Savior passed that way
He looked up in that tree
And He said, "Zacchaeus, you come down!
For I'm going to your house today
For I'm going to your house today."

Zacchaeus climbed the tree because his heart told him he needed what Jesus had to offer. Deep inside he knew he needed forgiveness and a new life. Jesus came to the house of the most hated man in town because he did not follow public opinion. He will eat with a Pharisee or a tax collector (or with anyone else, for that matter) because he came to seek and to save the lost (v. 10).

Jesus made the first move (v. 5). That's grace.
Zacchaeus welcomed him gladly (v. 6). That's faith.

Salvation could not be simpler than this. When Jesus calls, receive him gladly. Zacchaeus made a lifetime of mistakes and had many things to make right, but he was smart enough to come to Jesus. The little man with a big problem turns out to be the smartest man in town.