When you use the word "this" it is under that you are talking about more than one thing, even if you do not mention the other things. Usually to compare one thing to another thing. It saves time to not mention the other thing, but you can mention it to make your point clear. Here is what your sentence might look like when using the word "this" and you explain that you are talking about more than one thing: "Don't persist in THIS matter，you can't afford to offend them ！Persist in THAT matter instead." When you use "the" it is understood that you are only talking about one thing and only that one thing. I hope this helped. Feel free to ask for help any time