Titus of Bostra

Because the Lord had said, The kingdom of heaven is at hand, they that saw Him going up to Jerusalem thought that He was going then to commence the kingdom of God. When then the parable was finished in which He reproved the error above mentioned, and showed plainly that He had not yet vanquished that death which was plotting against him, he proceeded forth to His passion, going up to Jerusalem.

Catena Aurea by Aquinas ↗

Bede

And having said these things, he advanced, going up to Jerusalem. The parable being finished, he went up to Jerusalem, to show that the parable had been particularly about the outcome of this very city, which not long after would both kill him and, owing to the hatred of his reign, be destroyed by hostile calamity.

On the Gospel of Luke ↗

Bonaventure

And having said these things, he went ahead ascending to Jerusalem. Second, as regards intimating the person of the rebels, he adds: And having said these things, he went ahead ascending to Jerusalem, as if by this very deed he shows that he spoke the foregoing things on account of the Jerusalemites, who were going to deny that he was their king. For which reason also there immediately follows an account of how he came as king into Jerusalem, sitting upon a donkey. But after that great glory he had to endure insult. …

Commentary on Luke, Chapter 19 ↗