What is the meaning of these two sentences from "The Tyger" in Songs of Innocence and Experience? What is the meaning of these few sentences in...

It is key to realise that in this great poem that is part
of Blake's stunning collection of poetry, Songs of Innocence and Experience, the speaker
is so impressed and overpowered by the tiger and its strength and might that he asks a
series of rhetorical questions, asking what immortal being, divine or demonic, could
have created such a fearsome creature and how. These questions are never answered, but
the two quotes that you have highlighted are some of these rhetorical
questions.

The first quote you have highlighted uses an
implied metaphor to compare the process of fashioning the tiger to a blacksmith forming
something out of metal. Note that the "hammer" is refered to and then the speaker asks
what kind of "furnace" could have been used to fashion the brain of the
tiger.

Likewise, the second quote asks what the motive was
for creating such a creature as the tiger and questions the identity of the person that
"seized the fire," metaphorically bringing the tiger to
life.

It is important to realise that all of these
questions remain unanswered. We are still left pondering the symbol of the tiger and the
power, strength and terror that it represents.