TL;DR; The bolded text achieves something a 'softer' text doesn't achieve. An audit is also a way of providing feedback to the reviewer. A system with different 'severity levels' can and will be gamed.
I disagree that the message should be changed. The text STOP! Look and Listen. is meant to grab your attention, to make you stop reviewing for a second and to make you read the question to understand why the correct1 action should have been taken on this review. It grabs your attention like no other 'softer' message would do. Because it is short and because it is so to the point, it feels like:
- They are being serious about it
- You should re-read the question to figure out why this question was handled different than you wanted.
- You've failed an audit. You should feel like you've failed an audit, because people don't like failing anything. It should put you on your toes. You should feel that you have to be more careful when reviewing other questions to avoid failing more audits.
You don't see if you 'fail' to correctly review an other item in the queue apart from the audits, unless you decide to go through your own reviews and see what other people choose. 'Failing' normal review items doesn't offend the system, but instead 'offends' real users who are angry that their question/answer were misjudged. That's worse, and because the reviewer can't get feedback on that, they should get feedback through audits instead. Therefore each individual audit that you fail should always make you feel that you failed it, to achieve above 'feelings'. The actions taken on a failed audit (e.g. review ban) will however be less severe or non-existant if you have more 'good' audits.
For those reasons a message like Could you please take a minute to read this text about failing an audit. would not work. Sure it is a lot more friendly, but it also feels they are not serious about the message they try to tell you. Therefore while reading the messages you don't feel like you should change something about how you review, if you obliged to read the message at all. It would feel like they can't care less about how you review.
If you review a lot, you should know that you should read a failed audit as criticism, and handle it accordingly. You read it, you take the important things out of it that you want to do better next time, then you let it go. A review audit is not to discourage you from reviewing, but to make you better in it and/or force you to always pay close attention to what you are reviewing.
As for the text below the bolded text, I believe it already says something along the lines of "Don't worry, this question was already handled accordingly, but please take a moment to re-read this.". The rest is just a plain description of what the audit is, what the result was of that audit and what the correct1 action would be on that audit. That's 'soft' enough for me.
An other concern of having a 'severity index' with incrementing more negative feedback, is that it allows people to game the system. Robo-reviewers can simply robo-review until you get the one-but-worse 'severity index' text, then properly review a few to wash away this 'severity index' and then continue robo-reviewing. I would not like that to happen.
1 What is correct according to an algorithm will never be 100% accurate with what a group of humans find correct.