Surat An-Nur (The Light)

Some background: several ayat from this sura were revealed to defend the wife of the Prophet (SAW), Ai'sha (RA) because of a misunderstanding in which people accused A'isha of something that wasn't true. What does this ayah specifically communicate about what the attitude of a believer should be? Why do you think its a quality of a muslim to assume the best of others?