Questions about the implementation in Job.do()

Hello, I am new to this library. While I am digging in the source codes for understanding the usage of this library, I cannot understand [this line][line1].

What is the purpose of [this line][line1]? Why is it necessary even [another line][line2] do it's job?

Thanks for your time

[line1]: https://github.com/dbader/schedule/blob/master/schedule/__init__.py#L461
[line2]: https://github.com/dbader/schedule/blob/master/schedule/__init__.py#L459

Start with schedule/__init__.py at lines 459 and 461, following the two linked lines in Job.do(). Read the surrounding method and related tests to determine why both lines are needed. Done means documenting the purpose of line 461 and how it differs from line 459.

Written by the indexing model from the issue text.