Before you submit your manuscript to a literary agent, you have been told countless times to make sure that the thing is ready for publication. That means you have to be the editor, or pay good money to have an editor slice and dice your prose. No misspelled words, no run-on sentences, no flaws in pacing, etc. etc. are allowed.
So imagine how clean your manuscript would be if someone at Zachary Shuster Harmsworth took you on as a client.
The literary agency is looking for an editor to work in house, to clean up manuscripts for ZSH clients.
Would you happen to have a friend with some experience at editing? This could be your foot in the door.
The position requires experience, so it's not as if you could offer to telecommute for free and edit whatever manuscript the agents sent to your computer inbox. So you'd have to line up an accomplice with the proper credentials. A person who owes you an enormous favor because you are going to ask for an even more enormous favor in return.
While said friend is working away, you would have him or her add your manuscript to the pile so that it would get under the nose of a likely party. Say you've penned a bit of women's fiction and Jane von Mehren might bite. She's relatively new to the agency and possibly in search of new clients with publication-worthy manuscripts. How convenient if your manuscript landed on her desk, bypassing the usual gates that have been closed to you.
Then again, if you had a friend with the skill to gain employment, someone with superlative publishing credentials, you would already have asked that friend to edit your manuscript or at least give it a quick glance to offer you some advice.
In which case, you really, really, really need an insider to get you in through the back door, because your brilliant prose just isn't getting the right attention.
And if you find such a one, would you find room for a second manuscript in your scheme? And then let me know where to send it so it arrives at the right time when the plot is launched.