In Coelho's The Alchemist, why does the author not clearly mention when the story takes place?

In Coelho's
, the author does not specifically state when the story takes place. In
fact, the book could take place at any time, for there are no references to
technology (telegraph, telephone or computer) or even world events that would allow the reader
to pinpoint a particular time in the history of the world. And it would seem that this make
perfect sense in light of the book's purpose: Coelho responds to a personal, spiritual awakening
that he experiencedas written in his novel, The Pilgrimage. In
The Alchemist he continues to share insights that he garnered from that
experience. His messages are timeless ones that are important to hear
regardless of the time period in which the story might have taken
place.

To me, one of Coelho's messages is that everything comes from the Soul
of the World (God) and everything will return to it:

...everything has its Personal Legend, but one day that Personal Legend will be
realized. So each thing has to transform itself into something better, and to acquire a new
Personal Legend, until, someday, the Soul of the World becomes one thing only. 

This also speaks to the constant state of change taking place in
the world everyday.

This oneness with the universe is
not a new concept by any means. The transcendentalists, for example, saw a clear connection
between man and the natural world, and the great capacity for human beings to exercise wisdom
beyond what might be expected from a mere man (or woman).

...transcendentalist literature also promotes the idea of nature as divine and the
human soul as inherently wise.

Santiago learns to
harmonize and understand nature, and he becomes wise beyond his years in paying attention to
what the world can teach him.

Another important theme is that everyone has a
purpose in the world even though many may never realize the truth of this:

No matter what he does, every person on earth plays a central role
in the history of the world. And normally he doesn't know it. 

Santiago learned a great deal from those who wished to help and advise him, as well as
those who took advantage of him or disagreed with his quest or his methods.

Another important message is that lovetrue lovedoes not try to
control the object of that love. The alchemist notes that Fatima, if she
truly loves Santiago, will wait for him. She will understand that he must
leave to pursue his Personal Legend, and in loving him sincerely, she will not try to stop or
discourage him in any way:

Love never keeps a man from
pursuing his personal legend. If he abandons that pursuit, it's because it wasn't true
love.

Finally, Coelho asserts that there is only one
power in the world. This power is the Soul of the World (God), and that this power can be found
in every corner of the universe, but especially in that of love. 

...everything under the sun is written by one hand only. It is the
hand that evokes love...

The story is not set in a
specific time period because the themes Coelho addresses in the novel do not
belong to one specific era: these are timeless themes
that have endured the rise and fall of powerful civilizationsbut they
remain unaltered.