The comma after job tells us that the phrase as directed is non-restrictive.
The comma after “job” tells us that the phrase as directed is non-restrictive.
The sentence states :you“you have been directed to do a job"job”, and implies that how you do it is up to you.
But if we take out the comma.
CompleteBut if we take out the job as directed.comma,
Complete the job as directed.
Now as directed“as directed” is restrictive, and the sentence is saying something more severe: Do the work, and make sure you do it the way you were told to do it.