A heifer loves to thresh because they can walk around freely without a yoke. Yahweh means that he has allowed the people of Israel to be free and have a pleasant life. (See: [[rc://en/ta/man/jit/figs-metaphor]])
Here "yoke" refers to suffering and slavery. Yahweh has been kind to the people of Israel, but the people have been unfaithful to him. So he will punish them and send them away as slaves. (See: [[rc://en/ta/man/jit/figs-metaphor]])
The irony here is that the "heifer" views herself as "fair"—that is, as beautiful and delicate—but Yahweh views her as ugly and so will put a yoke on her, which will destroy her beauty. (See: [[rc://en/ta/man/jit/figs-irony]])
Here "Judah" refers to the people of the southern kingdom and "Jacob" is the people of the northern kingdom. This means God will cause difficult times for both kingdoms. (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-metonymy]])