I am frequently in discussion with my friends who are Bible Christians. Please advice me on the best way to explain that the Bible is not the sole rule of faith. Thank you!
It is good that your friends trust in the Bible but even the Bible itself does not claim to be the sole rule of faith. Paul wrote, “[W]hat you have heard from me before many witnesses entrust to faithful men who will be able to teach others also” (2 Tim 2:2; emphasis added). And he instructed, “[H]old to the traditions which you were taught by us, either by word of mouth or by letter” (2 Thes 2:15; emphasis added).
These oral teachings and traditions have been handed down and entrusted to the Church so that they remain as much a part of the full Christian faith as the Bible. To ignore them is no less a tragedy than to ignore the Bible.
For more on this see Scripture and Tradition.