How did Zacchaeus place his full trust on the Lord, he was only willing to do the things that the rish young ruler was not able to do. Remember the rich young ruler who came to Jesus asking what he must do to inherit the kingdom of God? Jesus told him to keep the commandments which he confirmed that he does, so Jesus asked him to sell all he had and share with the poor which he couldn't.
So Zacchaeus did share with the poor and that's what it means faith in Jesus, if you don't, then you have denied the faith just as Paul says:
1 Tim 5:
7Give the people these instructions, so that no one may be open to blame.
8Anyone who does not provide for their relatives, and especially for their own household, has denied the faith and is worse than an unbeliever.
As you know, in ancient Israel wealth was specifically believed to be a blessing God bestowed on people due to their righteousness.
In Luke and Matthew Jesus turned this idea on its head with the rich young ruler from His very first sentence "No one is good save God alone" - not even a Man of God.
He went on to prove it, which left those within hearing asking, if this (think, righteous man so blessed by God) can be denied eternal life, how can anyone be saved? (let alone me!)
Jesus answer was to answer what is impossible for man is possible for God. meaninging, salvation is of the Lord, not something we are able to qualify for. We have all fallen short of the Glory of God.
Now with the tax collector, Jesus has another apple cart to overturn, another belief set that needs corrected. And that is the unclean sinner.
If you recall in Luke 10 one of the lead ups to the rich young man/ruler was the Pharisee and the tax collector praying, the Pharisee lifted his head to God and thanked Him for making the Pharisee so righteous, unlike the tax collector over there. And the tax collector humbled himself before God and threw himself on the Mercy of God praying God, have mercy on me, a sinner...
Jesus lauded the tax collector for humbling himself and recognizing his condition before God and relying on God for mercy. Something from the least to the greatest need to do.
So here with Zacchaeus whose another tax collector we see a similar situation as in Luke. We've got this tax collector, a sinner in the eyes of all, climbing the tree in hopes of seeing, and perchance speaking to Jesus, and all around shocked when Jesus decided to go to that man's house. (contact with such a person according to the Pharisees not done because he was ritually unclean) so there was shock and awe over such a societal taboo being upset.
So the man offers that he gives half of his earnings to the Temple, and Jesus declares him a son of Abraham (not one who is ritually unclean). Why? he was still a traitor, in the eyes of the Jews, as he worked for the Romans - but being a son of Abraham is more than everything they assumed it to be, and less than they assumed at the same time.
It requires a lot of faith when all your countrymen call you unclean, when no one will eat with you, speak to you, to give half of all you have to a God everyone's spent your adult life telling you hate you. That's faith, that's a man whose heard something new, and that something, even though he didn't hear it yet with his own ears has acted in faith upon those words.
That man had some serious faith. More than I for real - and Jesus stayed with him because here was a man who had the faith of Abraham.
I was far mod like Jacob, willing to wrestle until I got the satisfaction of understanding, but this guy? This guy took it on faith and ran with it.. that's a greater faith I think, and so Jesus blessed him for it, and called it the faith of Abraham. It should bring a tear to everyone's eye, it does mine, that faith like that exists. It's joyful to see, we should all be more like that guy.
But it's not the act per se we need to look at, but the faith which caused him to do it. That is what was blessed and acknowledged.