"Puritanism may have set certain limits on the American imagination." Please explain it."It was also one of its essential roots."

It seems to me that the subtext of the question might be
better to appear with the initial quote.  That being said, there might be two parts to
the answer.  The first deals with the limitations on imagination with regards to
Puritanism.  I think that the fear of sin and the overall fearful position in which
Puritans classified themselves in their relationship and understanding to God did limit
imagination to a great extent.  It is difficult and challenging to conceive of any
imagination or the expansion of it if one is in constant fear of how the divine will
react to it.  Puritans were gripped by this concept in their own consciousness and so
one can see how imagination would be limited.  However, in a very paradoxical way, one
could argue that this also served as a way to develop the concept of imagination.  For
example, in Salem, the fear of God and of witches caused individuals' imagination to run
amok in presuming that there are such things as witches and witchcraft present amongst
the townspeople.  Part of this happens because of the preoccupation with God and his
vengeance and the belief in original sin.  In the end, one can see the repression of
imagination due to a fear of the divine as well as an expansion of it when it comes to
different ways in which the holy powers are unhappy with
humanity.