Answer:
The character that said this quote was the father of Anne, Otto Frank. In his statement, I think he meant that “if we keep bickering and arguing, we are going to bring ourselves to destruction”, which basically means we are the true enemies to ourselves. In his statement I think he meant that if they keep fighting, they were only going to make the situation worse. In other words, they are the true enemies to themselves. I agree with this statement because if they were to fall apart from the inside, there would be lots more problems to deal with than just the Nazis. For example, everyone in the Secret Annex is trying to survive, and there is barely enough food to feed everyone. With someone trying to steal food, it only makes the situation worse with the fact that supply will run out quicker. Furthermore, with all the noise from arguing, they'll surely be found.