(Prabhupada's lecture - Śrīmad-Bhāgavatam 2.1.1-4 – Boston, December 22, 1969)
So we should be so much responsible, how to avoid such laws of nature. We can have any form of life out of 8,400,000 species that are before you. You should always remember that "If by chance I slip to one of them, then how I have wasted my time." This is responsible life. Labdhvā su-durlabham idaṁ bahu-sambhavānte. Bahu-sambhavānte means after many, many appearances. This is appearance. This body, present body, is one of the appearances. It will never appear again. He'll... I will have to or you will have to appear in a different body. But this human form of life is a great opportunity. Bahu-sambhavānte. Bahu means many, and sambhava means appearance. After many, many appearances, we have got this. Labdhvā su-durlabham. Su-durlabham. Su means very costly. Durlabham means to gain with great difficulty. This responsibility must be there in the human form of life. Labdhvā su-durlabham idaṁ bahu-sambhavānte. After many, many appearances. And what is this? Mānuṣya, man, human form of body. Artha-dam: and you can achieve a great success in this life. This is the hint given.
Therefore for that great success everyone should try his best. And one may think that "Now we are young men, young boys and girls. Let us enjoy life." And that facility is very much easy to obtain in your country. In the school, college or society, the young boys and young girls, they have got ample facility for enjoying material life. Enjoying material life means sex life. So Bhāgavata says, "No. You should immediately try for the ultimate success of your life. Don't spoil your life." If we become absorbed in the thoughts of materialistic way of enjoyment, then naturally we have to take birth again in any other form of body, may be human body or may not be human body. But unless we purify our mind and consciousness, we must have to accept the material body.