'Upavasa' means to fast. 'Vasa' may mean to reside and 'upa' means nearby. So upavasa means "to reside nearby". So the main principle of Ekadasi is to reside near the Lord. It is not about fasting but about coming closer to the Lord. This is the actual heart of the idea. In fact, every day we should come closer to the Lord but two days have been singled out to emphasize the point. So we can call it Hari's day and everyone will be told to do certain observances. But the purpose is to reside closer to the Lord, to come near to Him. We may start with Ekadasi (two days a month) and then end up doing it every day. That is the real idea.
RE: "It is not about fasting but about coming closer to the Lord"
'Fasting' is one of the 'tools' that we use,
to come closer to the Lord.
Also, 'fasting' helps us to achieve
mastery over physical impulses; also reducing the
metabolic activities of the body; allowing the
mind to concentrate more freely on the object of our devotions.
Another tool is quiet surroundings. I think Thakurji or Swamiji once said: "One cannot meditate at the crossroads of a busy highway" [inexact quote]
Of course, activities, such as 'fasting', must be carefully managed. One must have adequate nourishment, especially when leading an active life in the modern world.
