Purport

Now when explaining different ways to practice Bhakti or devotion, Bhagvan Shri Krishna said the best is for you to fix your upon me(Shri Krishna), and engage all his intelligence into me alone. Talking this sentence to apply to humans, the best for any devotee is to devote himself completely to Shri Krishna. By doing so human directly achieve Shri Krishna and is out of any effects of this mortal world.

Now important is to understand what it means by fixing the mind and engaging all intelligence in Shri Krishna and how to achieve that. There is no easy way to explain it, but it can be understood by taking some examples. We have devotees like Meera Bai, Shri Chaitanya, Shri Tulasida, Shri Surdas, Shri Raidas, Shri Madhvacharya, etc.
When we go further we find many other examples from our scriptures. From Ramayana, we know about Mata Sabari, who dedicated every single day putting flowers thinking Shri Ram will come to her house. And it happened that Shri Ram indeed came to her. We have examples of Bhakt Prahalada and Dhruva.

When we talk of these personalities only thing we know is that there whole life devoted do Shri Krishna, everything they did, every thought they had, every word they spoke was related to Shri Krishna. They have no other identity. Perhaps they did not do anything other than.

So when a human loves Shri Krishna so much that Shri Krishna becomes everything for him, then whenever he thinks he thinks of Shri Krishna, whenever he speaks it becomes either bhajan or poetry related to Krishna. This state for the human is the highest state of devotion.

Narad Bhakti Sutra has given the definition of Bhakti, which is:
“It is the offering of all acts to him and feeling the highest pang of separation on the occasion of losing remembrance of him”
Narad Bhakti Sutra#19

Further, Narad describes, the devotion is such that is become both action and fruits in itself
“But the son of Brahmā(Narad) says that bhakti is its own fruit”
Narad Bhakti Sutra#30

Therefore for such a devotee, devotion to Shri Krishna is the only action he knows, and then he gets further devotion as the fruits of his devotion as actions. This

When a human reaches that state, he gets united with Shri Krishna and remains in Shri Krishna’s abode forever and ever.

Such devotion to Shri Krishna is however difficult but is the best of all devotions.

In the next Shlokas Bhagvan Shri Krishna described Arjuna other ways of practicing devotion.