Apara Ekadashi takes place on Vaishaak Vad 11. On one occasion King Yudhistir enquired to Lord Krishna, “O Krishna, please enlighten me with the importance of keeping vratt on Apara Ekadashi?” The Lord replied, “The greatness of observing the vratt of Apara Ekadashi has been described in detail as follows in the Brahmand Puran: 

Apara Ekadashi is the giver of good deeds, destroyer of sins and one who observes the vratt with a full fast on this day attains great esteem and honor in this world. Any sins which have occurred in their daily life, socially or while running ones business, are cleansed through this vratt of Ekadashi. Many devotees go for tirtha snaan (holy bathing in various great rivers, lakes and oceans), pilgrimages to all holy places, grant various donations and such other great deeds but none of these balance with the vratt of Apara Ekadashi. 

The vratt of Apara Ekadashi removes any committed sins just as sunlight eliminates darkness. On the other hand, one who does not perform the vratt of Ekadashi suffers great distress and goes through vast difficulties in this life and the next. 

One who follows the vratt with full faith to Almighty God is freed from all attachments in this world and ultimately achieves the heavenly abode.