Why is it important for an HR manager to understand the context and environment in which she or he operates?

We won’t do your homework for you. A simple 2 minutes search brought up these sources.

https://www.thebalance.com/how-to-prepare-for-a-career-in-human-resources-1918347
Read through this. Some of your answers are here.

More answers here. https://hiring.monster.com/hr/hr-best-practices/recruiting-hiring-advice/job-descriptions/human-resources-manager-job-description-sample.aspx

Read between the lines, and/or do a little more searching, and you should be able to sort out the rest.

Think about the job description of someone who works in HR. It should be pretty self-explanatory. What @snowberry said is helpful aswell

Do you know what HR managers do? If not, look that information up first.

It should be very clear to you why they need to understand the context in which they work, when you understand what they do. So start with the definition of an HR manager’s job description and tasks first.

Can you see how being an HR manager in a hospital would be much different than having that same position in an oil refinery? And just for fun, one of those would certainly require knowing Spanish.