What is the meaning of this comparison?

Maharsha: The Ganav fears judgement below but not the judgment above. It is as if he denies the Divine supervision of this world and reward and punishment. The Gazlan does not deny any of that. Rather, he ascribes more importance to his benefit from the theft than the punishment in this world and the next.

Is it not better to sin in private?

Maharal: The Gemara (Moed Katan 17a) writes that if a person's desires overcome him, in order to avoid Chilul Hash-m he should go to a place where he is not known, in order to sin. That would imply that it is actually better to sin in private. He explains that that is referring to a person who cannot resist his desire, but here, if he was able and he sinned in private, his punishment is greater.

Why does R. Yochanan ben Zakai make a second comparison, saying that the Ganav is 'making it as if the ear cannot hear'?

Ben Yehoyada: He should have been concerned for the victim's cries for Divine justice, as the Pasuk says (Shemos 22:22), "for if he cries out to Me, I will surely hear his cry". But he has denied this and implied that the ear cannot hear.

Chasdei David: The eye alludes to an actual Ganav and the ear alludes to a To'en Ta'anas Ganav - one who claims that a deposit that he was guarding was stolen but he in fact took it himself.

What is a deeper understanding of this parable?

Rif: If a Ganav swore and then admitted that he stole, he must bring an Asham (guilt) offering. But if he did not admit, he has invited the people of the city, i.e. he will need to pay Kefel (double) to the victim of his theft. However, he does not give the children of the King, i.e. the Kohanim, as they do not receive his Asham. In contrast, a Gazlan does not pay Kefel nor bring a guilt offering if he admits, so he did not invite the people of his city nor the children of the king. Therefore, the Ganav, who must pay Kefel to the city people, will need to pay 4 or 5 times if he slaughtered or sold it and did not admit; since he did not invite the children of the king.

When he only stole but did not slaughter or sell it, whether it was a sheep or an ox, he must pay double. Why does the Torah not require paying more for an ox than the sheep in that case, if the thief interrupted the ox's work?

Rif: Perhaps it is only considered stopping its work when the animal is actually slaughtered or sold, but if it was merely stolen, it is only a temporary interruption.

Perhaps he stole it when nobody was around, so why was he disgraced by carrying it?

Maharal: Even though nobody saw the Ganav carrying the sheep on his shoulder, he was disgraced in his own eyes.

Why did R. Yochanan ben Zakai expound differently from R. Meir?

R. Noson Gestetner: Both of them were concerned for disgrace. R. Yochanan ben Zakai focused on the disgrace of the thief. R. Meir focused on the disgrace of the ox owner. Since the Gemara in Nedarim 49b teaches that 'work is great as it honors the one who does it'; the owner is now disgraced because he cannot work.