“... If the only tool you have is a hammer, you'll treat everything like a nail"
What does this quote mean to you?

It means that you would handle everything very harshly, almost like how you need to be aggressive when hammering a nail. The hammer is probably a metaphor for the temperament you use to handle things, if that makes sense.

Explanation:

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“There are those who are asking the devotees of civil rights, ‘When will you be satisfied?'”

Explanation:

I think this is the correct answer because Matin Luther King Jr. is making reference to those people who question the devotees, in other words the followers. To the opponents of King's ideas, it seems that the devotees will never be satisfied as they are allways fighting and asking for more. That is the reason they ask them "When will you be satisfied?" The opponents don't perceive  the end of their demands.

Martin Luther King asks his followers to fight for things that at that time may have seem imposible, that is the reason the expectations seem high.