Why did Jesus have dinner with Zacchaeus? - Answer

He invited himself to dinner to finish the picture, since when he came off the cross, he went to the marriage supper of the Lamb.

As a bride of Christ figuratively, the actions of Zacchaeus giving away his possessions and restoring what he had taken completes the picture since Christ and his bride are 'fruitful'.

Jesus sees the hand of the Father in the intimate details of what happened and declares salvation because of the presence of the hand of God in it all.

We too are chosen to be types of Christ and God works in the details of our lives to make us look more like Jesus every day.

'Why' is always because God chose to, 'How' is always the cross. There is no merit toward salvation in giving things away, nor by giving up his job, nor by being called down from the tree. Jesus was merely declaring what God had done by the fruit that he saw.

Scripture

Lu 19:7 And when they saw [it], they all murmured, saying, That he was gone to be guest with a man that is a sinner.

Lu 19:8 And Zacchaeus stood, and said unto the Lord; Behold, Lord, the half of my goods I give to the poor; and if I have taken any thing from any man by false accusation, I restore [him] fourfold.

Lu 19:9 And Jesus said unto him, This day is salvation come to this house, forsomuch as he also is a son of Abraham.

Lu 19:10 For the Son of man is come to seek and to save that which was lost.