Bhagavad Gita Verse 31, Chapter 4

yajnyashishtaamritabhujo yaanti brahma sanaatanam |
naayam lokostyayajnyasya kutonyaha kurusattama || 31 ||
 
Only those who taste the nectar of sacrificial remnants obtain the ever-existing eternal essence. The non-performer of sacrifice does not have (joy) in this world, how (will he get joy) in other worlds, O foremost among Kurus?
 
yajnya-shishtaaha : remnants of sacrifice
amritabhujaha : those who have tasted nectar
yaanti : obtain
brahma : eternal essence
sanaatanam : ever-existing
na : not
lokaha : in this world
asti : have
ayajnyasya : non-performer of sacrifice
kutaha : how
anyaha : other worlds
kurusattama : O foremost among Kurus
 
So far, Shri Krishna gave us a wide range of yajnyas that we can implement in our daily lives. In this shloka, he urges us to implement at least one of those yajnyas in our life. He says that one who does not live his life in the yajnya spirit will not even be able to function properly in the material world, let alone progress on the spiritual path.
 
Let's take a practical example. Suppose we decide to follow the yajnya of nityaahaarah. In other words, we decide to restrict our food intake. How do we actually implement this? Shri Krishna tells us that in all actions that we undertake, we should first perform the yajyna, and then partake of the "remnants" of the yajnya.
 
So if we see a tasty dish, we perform a yajnya on the spot by saying "I am performing a yajnya. I first offer all the food to Ishvara because this food belongs to Ishvara. I will take only x amount for myself as the remnants of that yajnya." The key point here is we first perform the yajnya, then partake of the fruit of the action. We do not rush directly into the action. This lets our intellect override the impulses of our senses.
 
If we truly make yajnya spirit a part of our life, we will develop "praasada buddhi", which is one of the cornerstones of karma yoga. Since the praasaada is a gift from Ishvaraa, we will not compare it to someone else's prasaada. In doing so, we will subdue negative emotions such as jealousy and insecurity. Over time, we will find inner joy in conducting such yajnyas every day. This inner joy is called "amrita" or nectar in this shloka. It will have the power of negating all our sorrows.
 
One who does not maintain the attitude of yajnya goes against the laws of nature, as it were. This is because the yajnya spirit pervades the entire universe, as we have seen earlier. Such a person lives an unhappy existence even in the material world, and has no chance of attaining any spiritual goals whatsoever.