Discuss Hermione's comment after Umbridge's banquet speech ("It explained a lot . . ."), and compare Harry's difficulties with Umbridge to his difficulties with Snape.

During the welcoming feast of Harry's fifth year at Hogwarts, Dolores Umbridge, the new Defense Against the Dark Arts teacher, interrupts Dumbledore to give a long winded speech filled with disturbing rhetoric. In particular, she states that certain things will be discouraged (that have been acceptable at Hogwarts thus far) and implies that teaching at Hogwarts will become far more dogmatic. Hermione (known to have quicker wits than her friends) is immediately disturbed by this language. She says that the speech explains a lot in regard to the stance that the Ministry of Magic is taking on the alleged return of Voldemort. She tells her friends that it means that the Ministry will be heavily involved in education at Hogwarts as they never have been before. This is an entirely new type of challenge for Harry. In regard to his previous difficulties with Snape, Harry's conflict with this teacher was entirely personal. Snape holds a grudge against Harry for the way that Harry's father treated him, but we could always assume that when the chips were down, Snape would do the right thing and was, at the very least, loyal to Hogwarts.
The conflict between Umbridge and Harry, on the other hand, is entirely political. Umbridge has no concern whatsoever for Harry personally, but is entirely consumed by what he represents in terms of free thinking among the students and a possible revolt against the ministry.
Umbridge is an extension of the ministry in terms of how she is consumed by paranoia and wants to deny the existence of Voldemort completely. This is a very significant moment of maturation for Harry in that it is the first conflict he has faced in which the lines between good and evil are totally blurred and the morality of the situation is somewhat subjective.