A 4 point assurance letter is a very basic survey / inspection of a homes Roof, HV/AC, Electrical, and Plumbing systems for the purpose of obtaining insurance on a home.  This inspection is sometimes required by an insurance company prior to insuring homes that are over 30 to 40 years old.  These inspections should not be construed as a full inspection report.  These inspections are typically 1 to 2 pages (a full inspection is normally 15 to 25 pages long) in length and written as so an insurance company knows what they are insuring.  Occasionally an insurance company will require improvements prior to issuing insurance on a home based on the report.