system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What is the purpose of a NumLock key?

In what world would anybody need to deactivate their numpad?
gpt
NumLock and ScrollLock both exist for those people who are spreadsheet ~~Archmages~~ experts

The number pad is by far the fastest way to punch numbers into a spreadsheet repeatedly, that's why it exists.  Having access to arrow keys on the same hand speeds up navigation of nearby cells while access to Home (go to the left-most cell), End (goes to the right-most cell), Page up, and Page down speed up access to distant points on the sheet.

Scroll lock is another key that exists almost solely for navigation of spreadsheets.  If you are in Excel and you turn on ScrollLock you can use the arrow keys to move the screen without losing the cell that you're in so you can pan up and right to see columns/rows you may be missing but still be able to type in your selected cell.  Again, just a key that exists almost solely for improved navigation in spreadsheet programs

So your next thought is, why do we need keys for this?  You can clearly just use the mouse to move around or click on the cell you want

Except for many years you didn't have a mouse.  Back in the before times, a lot of "computers" were terminals that accessed a mainframe and timeshared, LANPAR was a spreadsheet program for Mainframes back in 1969.  Microsoft DOS didn't support a mouse until 1982, and mice were uncommon until around 1985.  That's about 25 years of spreadsheet programs being in common use without mice being in common use.