What is the importance of Masjid al Aqsa for Muslims?

With regards to Masjid Al Aqsa, I cannot do justice in a single response and suggest that you read all the literature regarding this Masjid. I can mention that it is sacred to the Muslims; it is one of the three Masaajid which the Prophet (ﷺ) encourage us to travel to and that one receives additional reward for praying in it.