You said it, Baldock.

"To die, sweet Spencer, therefore live we all;/
Spencer, all live to die, and rise to fall."
- IV, vii, 110-111

This is my favorite line of the play. It speaks to me. Isn't this, in the end, what tragedy is about? This all-things-must-pass mentality. Baldock is looking at all that has transpired, and is coming to terms with the fact that there's virtually know way they'll make it out of this alive, considering what's already happened to Gaveston, and that the Queen and her minions have already driven them out of England proper. He is now resigned to his fate, it is inescapable at this point, much like death in general. The idea that all those who rise must eventually fall is repeated throughout the play; Gaveston came from nothing to achieve a powerful position, Edward's father died and he thus became king. But, as if part of this inevitable cycle of life, all eventually fell; Edward into exhile, Gaveston to death, Pembrooke, etc. to death as well. The impermenance that Baldock is talking about is something that we should all take note of: no matter where you are in life, it can never last.
I mentioned the Queen. She is growing in this act to become a truly major player in the politics of it all, whereas before she was notihing more than a woman griping about how her husband is in love with another man. Now however, her character has shifted to a disctinct desire to place her son in power,a nd thus consolidate our own. Her relationship with Mortimer has also grown, to something that her son seems distressed about. Mortimer it seems desires to succle on the princes power as rightful heir through the seduction of his mother. But, it's like Baldock was saying, when someone rises, they must eventually fall.