Bhagavad Gita Verse 36, Chapter 18

sukham tvidaaneem trividham shrunu me bharatarshabha |
abhyaasaadramate yatra duhkhaantam cha nigachhati || 36 ||
 
Now, listen also to the three types of joy from me, O foremost among Bharatas, in which one enjoys its practice and attains the end of sorrow.
 
sukham : joy
tu : also
idaaneem : now
trividham : three types
shrunu : listen
me : from me
bharatarshabha : O foremost among Bharatas
abhyaasaat : practice
ramate : enjoys
yatra : in which
duhkhaantam : end of sorrow
cha : and
nigachhati : attains
 
At the end of the day, the end goal of any endeavour or action is to eliminate some type of sorrow, whether it is in the short term to remove hunger, or it is in the long term to prevent financial instability in our family. The lifecycle of an action begins with Vaasanaas. These Vaasanaas or deep rooted impressions create thoughts, some of these thoughts become desires, and consequently, desires become actions. When the action is complete and the target of the action is attained, the desire subsides, and the mind is free of desires for a split second. This stillness of the mind results in joy.
 
Shri Krishna says that even this joy obtained as the result of an action is in the realm of Prakrirti. Any by product of an action is in the realm of Prakriti since actions themselves are in Prakriti. So therefore, this joy can also be classified into three types, which are saattvic, raajasic and taamasic. This also mean that the type of joy obtained is closely related to the knowledge, doer and action behind obtaining that joy. A taamasic action will not result in saattvic joy.
 
Shri Krishna also adds that the complete end of sorrow is only obtained through saattvic joy. This is because the other two types of joy, raajasic and taamasic, are mixed and impure respectively. They either have a tinge of sattva, or none at all. Furthermore, saattvic joy is such that having tasted it even a little bit, one becomes so attracted to it that one delights in performing actions that result in sattvic joy. That is why, saattvic joy is described in detail in the next shloka.

Bhagavad Gita Verse 12, Chapter 12

shreyo hi jnyaanamabhyaasaanjnyaanaaddhyaanam vishishyate |
dhyaanaatkarmaphalatyaagastyaagaacchaantiranantaram || 12 ||
 
Knowledge is superior to practice, meditation is superior to knowledge, and renunciation of fruits of actions is superior to meditation, for peace immediately follows renunciation.
 
shreyaha : superior
hi : for
jnyaanam : knowledge
abhyaasaat : practice
jnyaanaat : knowledge
dhyaanam : meditation
vishishyate : superior
dhyaanaat : meditation
karmaphalatyaagaha : renunciation of fruits of action
tyaagaat : renunciation
shantihi : peace
anantaram : immeditately follows
 
The last four shlokas laid out a series of stages that enable us to access Ishvara based on our qualifications. They were laid out in descending order, addressing the most qualified to the least qualified. Jnyaana yoga was prescribed for those who have given up attachment to the body, abhyaasa yoga for those who can sit for meditation, bhakti yoga for those who can perform every action for Ishvara, and karma yoga for those who can dedicate the results of their actions to Ishvara.
 
Here, Shri Krishna provides a recap of those four shlokas as well as providing some additional insights into the nuances of each stage. He first says that knowledge is superior to practice. Here, practice refers to mere mechanical chanting of japas without the involvement of the mind or the intellect. Such inert practice will not lead us anywhere. Shri Krishna cautions us against jumping into meditative practice without the knowledge of what we are doing, how to do it, what is the goal and so on.
 
Next, he says that meditation is superior to knowledge. Here, the word meditation is used in the sense of a higher kind of knowledge, one that does not create a distinction between the knower and the known, one that is a direct, intuitive understanding of Ishvara. This higher kind of knowledge is superior than dry, academic knowledge gained through a cursory reading of the scriptures without the guidance of a guru, and without the perfect internalization of that knowledge through a pure mind and intellect. In this sense, meditation or higher knowledge is superior to purely academic knowledge.
 
Now to get to these two stages, we have to take stock of our qualifications. Shri Krishna knew that the majority of people would have a great sense of attachment to the body, as well as a large stock of selfish desires that prompt them to selfish actions. They need a technique that is appropriate for their qualifications, and that will bring them to a stage where they can eventually practice meditation. For such individuals, renunciation of the fruits of actions, or karma yoga, is superior than meditation. Only renunciation will bring short term peace through reduction of worry for the future, and long term peace by making us qualified for meditation.