What is the meaning of this quote? "law never made men a whit more just; and, by means of their respect for it, even the well-disposed are daily made the agents of injustice". full explanation of the quote

This quote is saying that even men who understand and practice law are not better people because of it. The first part says that "law never made men a whit more just" 'a whit more' means 'any more', and 'just' means honest or good. So the first part means 'law never made men any more honest.
The second part says "by means of their respect for it, even the well-disposed are daily made the agents of injustice". 'This section basically means 'because they like law and respect it they have access to all of the inner workings and details, they are able to manipulate it to use law for their own injust purposes.

Basically, this is saying that men who know a lot about law aren't necessarily good and a lot of the times it just makes them more able to support injustices.