In "Young Goodman Brown," what caused Goodman Brown to become alienated from his previous life?

The answer to this question lies at the very heart of the
theme of this excellent short story. The severe and absolute transformation that Goodman
Brown undergoes thanks to his night in the woods is remarkable, and so we must look to
what happens during that night to explain the transformation. We can link it to the way
in which Goodman Brown sees so many supposedly stalwart and upright members of his
village involved with the devil. Note, for example, how Goody Close, the woman who
taught Goodman Brown his catechism is presented:

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But--would your worship believe it?--my
broomstick hath strangely disappeared, stolen, as I suspect, by that unhanged witch,
Goody Cory, and that too, when I was all annointed with teh juice of smallage, and
cinquefoil, and
wolf's-bane...

The
destruction of the various heroes of Christianity that Goodman Brown has looked up to
all his life certainly seems to underline the central message of the story, as delivered
by the leader of the devil worshippers, who says to the assembled
crowd:

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Depending upon one another's hearts, ye had
still hoped that virtue were not all a dream. Now are ye undeceived. Evil is the nature
of mankind. Evil must be your only happiness. Welcome again, my children, to the
communion of your race.

The
story thus points towards evil as an essential part of the human condition that cannot
be ignored or gainsaid. It is the discovery of this truth overall that results in
Goodman Brown's alienation from his former life and those around
him.