My take:
Harry has QQ(’s legacy) and Hermione to protect, and kills dozens of death eaters etc. etc. to make it happen
McGonagall has her students to protect, and commits publicly to doing so, no matter who their parents are, and takes up the role of headmistress (which we know she thought herself unsuited to) to do it
The students have themselves and future cohorts to protect, and commit to passing on QQ’s teachings themselves to do it
My take: Harry has QQ(’s legacy) and Hermione to protect, and kills dozens of death eaters etc. etc. to make it happen
McGonagall has her students to protect, and commits publicly to doing so, no matter who their parents are, and takes up the role of headmistress (which we know she thought herself unsuited to) to do it
The students have themselves and future cohorts to protect, and commit to passing on QQ’s teachings themselves to do it