“faith and morals”, a sufficiently flexible term to cover anything, everything and nothing.
“Infallibility”, For all the definitions no one seems to be able to recognize it if or when they hear it unless the one making the statement deems it so.
But unless the one making said statement is making an infallible statement then what they deem infallible may not be so.
Hard to understand? Since the whole idea makes no sense that’s true enough.
Are you trying to be infallible?
Understandability, by you or any person, is not a criteria for defining truth. At some point human capabilities must give way to faith.
As a logical matter, how can Luther’s doctrine of “the Bible ALONE” be the sole rule of faith, when it isn’t in the Bible?