[ByTheWay]

I'm having some difficulty understanding the difference between these two sentences:

ミルズさんはらいしゅうしゅちょうにいきます。

And

ミルズさんはしゅちょうに行くのはらいしゅうです。

Apart from the textbook stating that ...のは　is identfying everything before it as the topic of the sentence I'm in the dark.

Hope someone can help with this. Thanks for looking.