Kṛṣṇa says in the Bhagavad-gītā, ābrahma-bhuvanāl lokāḥ punar āvartino 'rjuna (BG 8.16). Even if, by activities, pious activities, or worshiping different demigods, you go to the Brahmaloka, where the standard of life is very, very great, life is also, duration of life is very, very great, so that is not permanent. But our problem is that we are permanent, eternal, and we are trying to be happy in the nonpermanent condition of life. My problem is that I am the spirit soul... Nityaḥ śāśvataḥ. I am eternal, śāśvataḥ. Na hanyate hanyamāne śarīre (BG 2.20). I do not die even after the annihilation of this body. Then where is my eternal body? This question should be raised by the human form of life. Athāto brahma jijñāsā.
Lecture on BG 9.5 -- Melbourne, April 24, 1976:
So we have to work here. So we can prepare ourself to being promoted to the higher planetary system or lower animal kingdom. We can become pig; we can become hog; we can become demigod; we can become so on, so on. Whatever we desire, Kṛṣṇa will give us opportunity. But that will not make us happy. If we go back to home, back to Godhead, without the tribulation of repetition of birth and death, that will make us happy. So our Kṛṣṇa consciousness movement is giving opportunity to everyone how to go back to home, back to Godhead, after giving up this body. One has to give up this body. That is certain. But why this body should be wasted for propensities like the animals? It should be fully utilized how to go back to home, back to Godhead. This is our propaganda, and we base on these authorities of Bhagavad-gītā As It Is. It is not that we have manufactured it. There is no question of manufacturing. It is authoritative. It is accepted by all the ācāryas. So our request is that you also take this opportunity and be Kṛṣṇa conscious, and next life you go back to home, back to Godhead, and be eternally happy.
Lecture on BG 13.1-2 -- Bombay, September 24, 1973:
So people, they want to enjoy life within this material world, but actually there is no enjoyment in the material world. Because, Kṛṣṇa says, there is birth, there is death, there is old age, and there is disease. So where is your happiness? After all, you have to die. Suppose I make very good arrangement, very nice house, very nice bank balance, very nice wife, children, everything, but death can come at any moment. Then where is your perfection? If after so much hard labor everything is ready for enjoyment, but I am called by Yamarāja... Mṛtyuḥ sarva-haraś cāham (BG 10.34). Death takes away everything. Therefore you cannot say the arrangement you made for happy life is perfect. That is not perfect.Just like children, we want to play without caring for future life. But it is the duty of the guardians to engage them in education so that in future they may be happy. Similarly, all the great sages, saintly persons, just like Vyāsadeva, Nārada, Devala, Asita, many, many great saintly persons, sages... Even Kṛṣṇa the Supreme Personality of Godhead comes to give us instruction so that we can become eternally happy.
- Srila Prabhupada
Lecture on SB 6.1.16 -- Denver, June 29, 1975: In this material world even if you go to the topmost planet, Brahmaloka, still, there is birth, death, old age and disease. Or you have to return back again. So this kind of going and coming back here is not good. Yad gatvā na nivartante (BG 15.6). If you go to such planet wherefrom you haven't got to come back again to this material world, that is highest perfection. That is Kṛṣṇaloka.So Kṛṣṇa says that "If you are working so hard to become happy in this material world, the same labor, if you worship Me, Kṛṣṇa, then you come to Me." Mad-yājino 'pi yānti mām. What is the benefit especially? Mām upetya kaunteya duḥkhālayam aśāśvatam nāpnuvanti: (BG 8.15) "Anyone who comes to Me, he hasn't got to come back again to this material world." So our Kṛṣṇa consciousness movement is teaching people how to go back to home, back to Godhead, Kṛṣṇa. That will make the people happy eternally. So in this life also, Kṛṣṇa conscious people, they are not unhappy. You can see practically. We are sitting in a very nice room and chanting Hare Kṛṣṇa and taking prasādam. Where is unhappiness? There is no unhappiness. And other processes, they have to undergo so many unhappy processes. Here, Kṛṣṇa consciousness, there is nothing unhappiness.