A Catholic supplement to the Bible. Despite the fact that many Catholics (and Christians for that matter) rarely read the Bible, much less the catechism, BOTH books are incredibly important to understanding the Catholic faith.
It is analogous to reading the Tanakh, the Mishna, and the Talmud - which is what studious, ambitious, pious Jews do to develop their faith and be better Jews.
Similarly, reading and understanding the Bible AND the Catechism of the Catholic Church will strengthen the faith of Catholics.
All Catholics should be knowledgeable in three things: the Bible, the Catholic Catechism, and Sacred Tradition.
These three things will take us far.