Symbolism, Imagery, Allegory
When Wolsey is finally confronted by the nobles, Norfolk tell him "To render up the great seal presently / Into our hands" (3.2.282-283). Why is everyone so bent out of shape over the dolphin's loudest neighbor?
It turns out that "seal" refers to the Great Seal, a stamp symbolizing the king's approval on official documents. It was a special duty of the Lord Chancellor to carry the Great Seal so that people would know when the king signed off on something. Wolsey has been going behind the king's back and using the seal whenever he sees fit—without the king's approval.
That's a big deal: it shows that for all his posing, Wolsey doesn't actually respect the king's power. When he uses the king's seal without the king's approval, he's taking on the king's power for himself. This behavior also seems to reveal that power is what Wolsey is really after. He's not loyal to the king; he's only loyal to his own ambition.
When Henry demands that Wolsey give up the seal, then, it's not just so that he can have his special rubber stamp back; it's so that Wolsey will know that it's time for him to step down. The seal gave the Lord Chancellor power and legitimacy, but Henry doesn't want Wolsey to have any of those things anymore—seal included.