Pre-Arrival mail.....you likely may have passed Eligibility Assessment.....and need to complete Background Check before passport request.
When Background Check is started......the application status message in your online account for Background Check.....will change from (1) to (2)....below;
..
1.) Background Check: “Your application is in progress. We will send you a message when we start your background check.”.
2.) Background Check: “We are processing your background check. we will send you a message if we need more information.“
....you are in the final phase......so patience