My textbook says:

A deductive theory is said to be consistent if no two asserted statements of this theory contradict each other, or, in other words, if of any two contradictory sentences at least one cannot be proved.

The "in other words" is what confuses me, how can "no two asserted statements of this theory contradict each other" and "if of any two contradictory sentences at least one cannot be proved" mean the same thing? I've been stuck on this all day can you guys help me please? and please don't give me examples that are too complicated I just started studying logic