In Chapter 4 of Book the Third of A Tale of Two Cities, what aspect of Doctor Manette's character is revealed?

At this point in A Tale of Two
Cities, because he is "a notable sufferer under the overthrown system" Dr.
Manette has been allowed to attend the prisoners of the Revolution; and, in so doing, he
has grown resolute.  Now "his suffering was strength and power," and he feels that he
can be instrumental in effecting the release of his son-in law.  When he speaks to Mr.
Lorry, who is surprised as such purpose and strength in Manette, the doctor tells
him,

"It all
tended to a good end, my friend; it was not mere waste and ruin. As my beloved child was
helpful in restoring me to myself, I will be helpful now in restoring the dearest part
of herself to her; by the aid of Heaven I will do
it!”

Using his influence as
the "Bastille Captive," Dr. Manette has even become physician for Laforce, so he sees
Charles every day.  Mr. Lorry observes that Manette's pride has returned to him now that
he has a purpose. Among the terrors of the guillotine, with death all around him, the
brave doctor walked, "confident in his power, cautiously persistent in his end." 
Manette tries to get Darnay released, but for some reason his release was rescinded. 
Despite his futile attemps to arrange the release of Darnay, Dr. Manette still is not
suspected or brought in for questioning; he moves freely, almost like a
spirit.