Verse 8.4.3

तद्य एवैतं ब्रह्मलोकं ब्रह्मचर्येणानुविन्दन्ति तेषामेवैष ब्रह्मलोकस्तेषां सर्वेषु लोकेषु कामचारो भवति ॥ ८.४.३ ॥
॥ इति चतुर्थः खण्डः ॥

tadya evaitaṃ brahmalokaṃ brahmacaryeṇānuvindanti teṣāmevaiṣa brahmalokasteṣāṃ sarveṣu lokeṣu kāmacāro bhavati || 8.4.3 ||
|| iti caturthaḥ khaṇḍaḥ ||

3. Those who attain this Brahmaloka through brahmacarya become the masters of Brahmaloka. They can visit all worlds as they like.

Word-for-word explanation:

Tat ye, those who; era etain brahmalokam, this Brahmaloka; brahmacaryeṇa, through the practice of brahmacarya; anuvindanti, attain; teṣām era, for such people; eṣaḥ brahmalokaḥ, is this Brahmaloka; teṣām, for them; sarveṣu lokeṣu, to all the worlds; kāmacāraḥ bhavati, they can go as they like. Iti caturthaḥ khaṇḍaḥ, here ends the fourth section.

Commentary:

There is a wonderful statement in one of the scriptures that says scholars talk about sweets but they never taste them. That is to say, the scholars talk about things they know nothing about. The scholars, it says, get only takra, whey. But the yogīs are the ones who taste the kṣīra, the thickened, sweet milk. Unless you eat the kṣīra, how do you know what it is like? Similarly, you may talk very well about Brahman. What you say may sound very good. But unless you have the experience of Brahman, you can’t understand what it is like.

Here the Upaniṣad says, how do you get this experience? Through brahmacarya, self-control. The word brahmacarya means brahma carati—that is, one who is always at the level of Brahman. The scriptures say there are two paths open to us—śreyas, the good, and preyas, the pleasant, the attractive. One who practises brahmacarya will reflect on these two and say: ‘I shall not accept that which is merely attractive. I shall only have śreyas, that which is the highest.’

Religion does not come by magic. It comes through self-discipline, and that means a lot of hard work, sweat, and tears. You have to yearn for it and cry for it, saying, ‘Oh when am I going to succeed?’ Sri Ramakrishna would often have no sleep at night and no food for the whole day. Sometimes someone would have to force food into his mouth in order to get him to eat. He had no body consciousness. Moreover, he would never accept money.

The Upaniṣad says that if you practise brahmacarya you are free and everything is at your disposal. But, like Ramakrishna, your attitude is: ‘I don’t care for all this. I don’t want anything in all these worlds. I want only Brahman.’

Vedānta says, you are free because you feel you are one with everything. Everything is within your grasp. There is no barrier between you and the world outside. Now there is a barrier. We want to see something because we think it is separate from us, outside of us. But when this idea of separation ceases, we feel we are everything.