Dogma vs. discipline

People constistently fail to distinguish between doctrines and ecclesiastical commands. A good example of this is priestly celibacy. Priests in the Latin rite can not get married because the Church commands it (Mt. 16.19). This was not always so and could be changed. The specific sacrifice of abstention from meat on Fridays was also a discipline and, hence, rules regarding it were licitly changed. On the other hand, the restriction of the priesthood to men is an infallible doctrine (not all are); it will never be changed. A sad effect of not making this distinction (and not believing in it anyway) is that those who consistently lobby for certain changes in the Church such as the ordination of women are literally trying to change divine decrees.

Reaffirmations

This issue mostly concerns believers and it is this: the Catholic Church frequently restates that which she has already unequivocally defined previously. This is important because sometimes the timing of a formulation takes on significance. An example would be whether or not the Church's statement regarding the canonicity of the Old Testament deutero-canonicals first occurred at Trent and, hence, after the Protestant revolt.