What does the phrase 'on the rhetorical battlefield' mean?
It sounds to me like a description of 2 or more people having a debate, argument or lively discussion that is weak in substance, but that is full of inflated language. Excellent speakers can use rhetoric skillfully to persuade listeners that their position is correct. But it has to be used sparingly and with logical and intelligent substance underlying the argument. Some people are so good at "rhetoric" that the rhetoric itself becomes a battle of wits, or a battle of words. The substance of the argument goes out the window, along with logic and clear thought. It's difficult to describe rhetoric in a few words, but you might find links below as they are found.
In general terms, 'rhetorical devices' are methods or techniques for engaging and even persuading an audience, especially in respect to public speaking of some kind yet including written communication. Examples of rhetorical devices would be repeating an important phrase over and over and citing authorities that are well-known and much-respected by the audience being addressed.
Rhetorical questions are those where the person asking does not require an answer. Their objective is to stimulate, or guide, thinking and reasoning on a matter. Many bible characters used rhetorical questions when teaching, counselling and explaining matters. Jesus Christ's words at Matthew 11:7-9 are a good example of this.