Sefer Yetzirah, the Book of Creation as translated by Aryeh Kaplan, is a nearly impenetrable book, examining the theogony of G-d’s attributes. This book is written in a highly esoteric style. The Hebrew, while formally simple, is compressed and open to many interpretations.
Kaplan takes a decidedly mathematical and mystical approach to this work. He believes Jewish mystics used this work to induce numinous states. He may very well be right. The work also has a strong and unavoidable tone of magic; for example, astrology, largely forbidden in the Jewish tradition, is given a pass in the Sefer Yetzirah. In a note Kaplan explains:
There is a commandment, “There shall not be found among you… one who calculates times. In the Talmud, according to Rabbi Akiba, this specifically applies to one who calculates auspicious times, and a number of authorities accept this opinion as binding. This, however, only means that one should not make astrology a dominant influence in one’s daily life… when one is engaged in these mystical techniques this prohibition is not applicable.
So, astrology is a tool used in Sefer Yetzirah, but never is prime directive. Instead, the book of creation blends philosophy, midrash, astrology and earlier kabbalistic works in a melange. In the end, it really belongs only to itself; read it, and it will be more than apparent.