The Shukla Ekadashi prior to Vaikuntha Ekadashi was the day when Lord Krishna imparted the Bhagawad Gita to his greatest devotee Arjuna. This day is celebrated as Gita Jayanthi. It is also an important Ekadashi in many many parts of India, and of course to Madhwas.
On this day Lord Krishna spoke to Arjuna about the ultimate goal of human life in 700 verses in 18 Chapters.
The Bhagavad Gita is considered to be the greatest spiritual books the world has ever known. In a very clear and wonderful way Lord Krishna describes the science of self-realization and the exact process by which a human being can establish their eternal relationship with God.
I still remember singing the the first sloka in the Bhagavad Gita in my school:
dharmakshetre kurukshetre samaveda yuyutsavaha
mamaka pandavaschaiva kimakurvata sanjayaha
P.S: The SSVT temple lists December 12th as Ekadashi and Gita Jayanthi. However, the Uttaradi Mutta lists it as 13th. So, please verify the dates at the country you reside in.