Knowledge being the means for one to see oneness is glorified by Lord Krsna next.
na hi jñānena sadṛśaṃ pavitramiha vidyate |
tatsvayaṃ yogasaṃsiddhaḥ kālenātmani vindati ||4.38||
In this world, there is indeed no purifier equivalent to knowledge. One who has in times attained preparedness through karma-yoga naturally gains (knowledge) in the mind.
We keep hearing different sadhana - means for purification in the spiritual path, but what are those impurities we need to remove and why they need to be removed? Most people think impurity in spiritual path is in the form of pāpam, but it is not. In this 4th chapter itself verse 4.36 said that even the worst wrong-doer will cross the ocean of samsāra with ease by the raft of knowledge. Things like anger, greed, and jealousy are our impurities which can be removed by prayer, helping others etc, especially karma-yoga. But the original cause of those impurities is ignorance about oneself. And only knowledge can resolve it. Therefore there is no purifier equivalent to knowledge.
But certain purity of the mind one needs to have to become eligible for knowledge, in this case karma-yoga is the means. One who has gained the preparedness of the mind to make him or her competent to receive the knowledge is called yoga-samsiddhah in this verse. Such a person has gained purification of the mind, meaning that mind of the person is steady and enjoys a certain freedom from rāga-dvesa (like and dislike / bondage).
This preparedness is gained in time, may be long or may be short. There is no certain timing for that because there is nothing new here to be created. We are not adding some more qualifications on ourselves, in contrary we are removing obstacles which make us unable to see this limitless nature of ourselves. All we need to do now is to live our lives with the right attitude and pursuing knowledge. By this way, gaining knowledge will take care of itself, in time, we will gain it naturally - tatsvayaṃ kālena vindati, because what we are trying to gain is already there.
Next, Lord Krsna mentions about three important factors which direct us for knowledge's pursue.
śraddhāvāllabhate jñānaṃ tatparaḥ saṃyatendriyaḥ |
jñānaṃ labdhvā parāṃ śāntimacireṇādhigacchati ||4.39||
One who has faith (in the śāstra and in the words of the teacher), who is committed to that (knowledge) and who is master of one's senses gains the knowledge.
This is an important and often-quoted verse of the Gītā, "śraddhāvāllabhate jñānaṃ - one who has faith in the śātra gains self-knowledge." Śankara-ācārya introduces it by saying, "the verse points out the means by which this knowledge is gained without fail." Knowledge will definitely take place when the appropriate means is present. What are those means, because of which one will definitely gain the knowledge?
First, one must have śraddhā - faith in śāstra which is unfold by the teacher. Gaining self-knowledge is dependent upon this śraddhā because of which the śāstra is looked upon as a pramāna - means of knowledge. Pramāna means that which is instrumental in gaining pramā - knowledge, and should not create doubts. It doesn't mean blind faith which I trust the words of śāstra and teacher without resolving the doubts. Śraddhā is a pending verification for me to enquire further on the doubtful knowledge about myself.
Śraddhā alone is not enough, some people have full śraddhā but do not have necessary commitment. Perhaps, they do not see the benefit of this knowledge or they may not have discerned the problem of life. When there is no commitment backing up one's śraddhā, the approach or attitude of the person towards the pursuit will be lukewarm. What does commitment mean? When nothing is more important than this pursuit, everything that I do is for supporting this pursue only. The person who has this kind of commitment to the knowledge is called tatparaḥ in this verse.
Śraddhā may be there without commitment, and commitment may be there without śraddhā. And for some people both śraddhā and commitment may be there, but the person may still not make it. Why? Because his or her mind is not together with reference to the senses and their pursuits. Distraction from sense object stand in the person's way of gaining self-knowledge. So third requirement is saṃyatendriyaḥ - one whose sense organs are under control. If we always go by our fancies, we will find no time for this pursue, in the same time we are giving the status of reality to those fancies. When such a person also has śraddhā in the śāstra and is committed to this pursue, he or she will definitely gain moksa.