- From Catholic Dictionary, page 375
Since the earliest days of the Church, heresies have arisen. Essentially, a heresy is a denial of a truth which the Church teaches must be believed. Often, a heresy will arise out of a misunderstanding of what we believe as Catholics. Over time, these misunderstandings will grow as more people become confused about what we believe, and, eventually, the Church calls a Council at which the bishops declare what Catholics are required to believe. As Catholics, we trust that the Holy Spirit will guide the Church and not allow it to fall into error. Because of this, we are called to respect the teaching authority of the Church when she tells us what we are required to believe. When people fall into heresy, they reject that authority and, as a consequence, reject the guidance of the Holy Spirit. This is the true problem with committing heresy – you end up not just rejecting the Church but God Himself.