The best answer to this question was certainty.
whilst the rule of law results in equal application, its outcomes are not always equal ie some are treated harsher than others.
The rule of law doesn't always create fair outcomes (as above)
Logically justice cannot be achieved if the above two are not achieved.
By process of elimination, certainty is the best answer, but it is also the most logical answer. The application of the rule of law means that law will be applied consistently to everyone, regardless of status. This creates certainty over the law itself.
In short, its definitely certainty.