Kathy,
I understand what you are saying.  Certainly, when we think of our purpose
as depending on us and on our knowing what it is, we are baffled.  I imagine
that Moses, when he was called to lead the Israelites, felt much the same.
Abraham, when God told him to leave all he knew and go to a land He would
point out, I imagine that Abraham questioned himself about goin without a
map  or any knowledge of this place.
It seems to me that the biggest problem we have with our purpose in life is
to try to limit God to just a certain talent or area of our lives to say
that that is our purpose.    In Ecclesiastes 12:14 a wise man summed it up
this way,

"here is the conclusion of the matter:
Fear God and keep his commandments,
for this is the whole duty of man."

We could substitute the word "purpose" for duty.

Maybe we shouldn't spend so much time trying to figure out what God's
purpose of life is for us and just give Him our all in every area of our
lives.

Ned