“The Imām’s Final Letter” (Re-Recording) - Muharram 1446, Night 22 - IMEC (MD)

What was the content of perhaps the last letter which al-Imām al-Husain (peace be upon him) wrote, before reaching martyrdom? How can we understand this letter? How can we learn from this letter & apply what we learn in our lives?
Note: this lecture was given again & re-recorded, as the first recording wasn't too clear all throughout.