Catalysts Effect on Overall Rxn vs. Step of Rxn

[Nada AbouHaiba 1I]

This has to do with homework problem 15.95 in the 6th edition
For part of e of this question it says that a catalyst is speeding up the third reaction only and then asks what this does for the rate of the overall reaction.
The answer is that there is no change and I was just a little confused to as why the reaction as a whole doesn't speed up as well if a part of it is being completed faster than usual?
Thanks in advance!

[Angel Chen 2k]

A catalyst will appear in the steps of a reaction mechanism, but it will not appear in the overall chemical reaction since it is not a reactant or product. Catalysts would only lower the activation energy of a specific reaction since they are highly selective and would not speed up the overall reaction.

[Letizia Ye 4F]

This is also because the the third step of the reaction is not included in the overall rate expression. Thus a catalyst speeding up the third reaction doesn't actually affect the overall rate, as it would only lower the activation energy of the third reaction to make it faster, not the rest of the reaction that actually contributes to the rate expression.