How does Hawthorne use symbolism to get across the main point of "Young Goodman Brown"?

There are several different answers to your question. 
Here's the one I like best.

As you read the story, you'll
notice that almost nothing is certain.  Hawthorne uses ambiguity is almost all cases
when something strange is happening.  Here are some
examples:

As
nearly as could be discerned, the second traveller was
about fifty years old, apparently in the same rank of life as Goodman Brown, and bearing
a considerable resemblance to him, though perhaps more in expression than
features

This, of course, must have been an
ocular deception, assisted by the uncertain
light.

So saying, he threw it down at her
feet, where, perhaps, it assumed life, being one of the
rods which its owner had formerly lent to the Egyptian magi. Of this fact,
however, Goodman Brown could not take
cognizance.

When
we get to the end of the story, we discover that we don't even know if ANY of it
happened; in fact, it is suggested that Brown fell asleep in the woods and that the
whole experience was a dream.

So if it happened it might
not have happened, and it might not have happened at all
:)

What is important is that Brown exits the woods with NO
sense of ambiguity, with the conviction of all those he trusted since his youth are
hypcrites and sinners.  Of course they're sinners, but hypocrites?  Only to Brown whose
holds people up to an impossible measuring stick.

"The
enemy of the good is the perfect."