Note: This is a pretty short part compared to the others before this... Also, I don't want to bother really reading the textbook version that much cause it has a much different vibe than what's in Project Gutenberg.
The narrator decides to switch to Don Juan's side of things for us to see how he's faring. At this point, the prince is suffering and can't even crawl after being beat up by his two older brothers.
In the middle of his suffering, he remembers the Virgin Mary and calls out to her. He wonders what went in his brothers' minds that they did what they did to him, and says that he thought that they would be able to go back home together. He even thinks that maybe it's because of the bird, and if it was so, he would've gladly let them have it (probably since they were presumably going together anyway.) Despite the literal and figurative pain that he's feeling, he still prays that his brothers be blessed.
Then he moves to another topic in his prayer, and asks that he be humbly brought to Jesus (I didn't really get the meanings of the words used in this part here, exactly, but the common practice of Catholics, from what I know, is to ask Mary to intercede for them, so I think it's something similar here) and be forgiven of his sins. He also asks that when the time comes that he passes away (in that place, I guess) that his soul be cleansed by His blood.
While he's praying, an old man comes by and says that Don Juan should endure his current suffering, since it won't be long until he gets relief. After that, the old man goes and massages the prince, healing him enough to be able to stand.
Don Juan is then told to go back to the kingdom, as his father still hasn't been cured of his illness.
As short as this scene is, it does give quite a bit of insight into Don Juan's character.
For one, he still retains his habit of seeking help from a higher power when things go badly. As I have said before, I don't really subscribe to praying to Mary, but I do believe in relying on God. It goes against the tendency (at least for some people) to actually go and blame God rather than seek help through prayer.
(Of course, there are also people who treat God as some sort of divine vending machine, but we can see that's not the case here.)
Two, he could have, but he doesn't think ill of his brothers. Instead, he concerns himself with what their struggles might be, that they would have to resort to beating him up. And aside from that, he also hopes for their well-being despite what they did. That is also not a basic human response (which instead would be paying them back with something that would hurt as well).
Three, he doesn't think of himself as being so righteous. And knowing that, plus the possibility that he might very well die, he asks for forgiveness for his sins and cleansing for his soul.
I've said before that Don Juan has traits that people could emulate, and I believe that it applies a lot especially to Christians. I mean, for all we know, this might have been intended for that (although for Roman Catholics, since the Philippines is mostly Roman Catholic, after all.)