You should first understand what ‘Vaikunth‘ (in Indian mythology, referring to the abode of Lord Vishnu) means. Vaikunth is a place where there is no lack, or shortage; there is only abundance.
It is written in the Srimad Bhagawatam, that everyone in Vaikunth is Lord Narayana Himself (meaning that in such a divine abode, every soul is elevated to Divinity and appears as Lord Vishnu, the Supreme Consciousness that permeates all of Creation). You cannot distinguish who is the Lord (Narayan) and who is the devoted sevak (servant or devotee).
The word kuntha in Hindi means shortage. And a place where there is no lack, or shortage of anything, that is what Vaikuntha is. It is said that everyone in Vaikunth(Paradise) is in the form of Lord Narayana Himself.
Ekadashi is the eleventh lunar day (Tithi) between the New Moon and Full Moon.
19th December is Vaikunth Ekadashi, so you can fast and remain hungry, even though there is no scarcity. If there is shortage and you have to be hungry, then that is poverty. When there is no shortage of anything and everything is in abundance, and you are fasting, that is Vaikunth Ekadashi.
Did you know that the Moon affects the ocean? On Full Moon Day the waves are higher. Nearly 60% of our body is made up of water, and it has saline content, like the ocean. So the Moon has an influence on the body and anything that influences the body influences the mind as well.
And that is why our ancestors have said to fast on Ekadashi. Because when the stomach is kept empty the toxins in the body get cleared. Fasting has a purifying effect on the body. So if you fast three days before Full Moon then on Full Moon day you will not have any problems – this is the belief.
It is not necessary that you must fast on every Ekadashi but it is good if you fast for at least two to three days in a year.
It is one of the major festivals celebrated in the temples of Lord Vishnu, especially in South India. Apart from being an Ekadashi, this day also commemorates the attainment of Vaikuntha, the spiritual kingdom of Lord Vishnu by Nammalwar, a great devotee in the Sri Vaishnava sampradaya.
Read the Bhagavad-gita
Gita Jayanti normally falls on the same day as Vaikuntha Ekadashi. Gita Jayanti is the day when Lord Krishna instructed Arjuna in the essence of spiritual knowledge. Hence, reading the Bhagavad-gita is one of the highly recommended spiritual activities on this day.
There are two types of literature glorifying the Supreme Lord Krishna. One contains the glories about the Lord and the other is directly spoken by the Lord. Since Bhagavad-gita was directly spoken by Lord Krishna, there is no difference between the Gita and Krishna. Reading the Gita is as good as associating with Lord Krishna.
Please spend some time in reciting the verses of the Gita and understanding their meaning.
Visit a temple of Lord Vishnu
In most of the Vishnu temples, a special entrance called Vaikuntha Dwara is erected on this day. It is said that those who pass through this dwara on this auspicious day attain Vaikuntha. If you have Deities of Lord Vishnu, Lord Krishna or any other of His avataras (Lord Rama, Lord Narasimha etc.,) on the altar at your home, you can decorate the altar and Deities and perform a special worship along with your family members.
Keep a fast
Since this is an Ekadashi day, try to observe a fast. Fasting is not only beneficial to our body and mind but it also has a lot of spiritual benefits.
There are different levels of observing a fast and you may select a level according to your convenience. Click here for more details on the foods forbidden on Ekadashi, different levels of observing Ekadashi, breaking the fast, etc.