He was thinking of his mother, and only of her; and the feeling within him was as pure, and holy, and beautiful as the dream of an angel.

He wanted to save his mother from insult in the first place, and from a life of ceaseless drudgery in the second.
A legion of angels seemed to have encamped in his soul to give him strength for the great purpose in his mind.

His was a holy and a true purpose, and it was this that made him think he could "do wonders." What Bobby intended to do the reader shall know in due time.

It is enough now that he meant to do something.

The difficulty with a great many people is, that they never resolve to do something.