I am writing to provide an explanation for the gap in my employment history as indicated in my mortgage application. Mortgage lenders might request a letter of explanation for various red flags that come up in underwriting.Learn how to write one, and download a template. A letter of explanation consists of short descriptions you can use to fill in the gaps in your paperwork for your underwriter. A letter of explanation can clarify your financial situation and get you one step closer to qualifying for a mortgage.