The modes of nature are three: sattva-guṇa, rajo-guṇa, tamo-guṇa. So if you act in sattva-guṇa, then you will be promoted to the higher planetary system. Ūrdhvaṁ gacchanti sattva-sthāḥ (BG 14.18). If you act in the rajo-guṇa, then madhye tiṣṭhanti rājasāḥ. And if you act in tamo-guṇa, then jaghanya-guṇa-vṛtti-sthā adho gacchanti tāmasāḥ. Jaghanya. Tāmasāḥ means very abominable activities. The other day I was speaking. I saw one gentleman, Indian gentleman. He was eating the intestines of hog in the airplane. That is very palatable, they say. Tamo-guṇa, most tamo-guṇa. Hog, the stool-eater, and its intestine, that is cooked, and he's eating. How much tamo-guṇa. Jaghanya. Jaghanya guṇa-vṛtti, very abominable. So next life he is going to be a hog. This is going on. We are in this material nature. Puruṣaḥ prakṛti-stho hi bhuṅkte prakṛti-jān guṇān (BG 13.22). We are in this material world according to our association with different modes of nature. We are making one type of mentality, and at the time of death, that mental position is responsible for carrying me in a different type of body. In this way we are changing body one after another.
So we are spirit soul. This is the chance of rectifying or purifying our existence. If we like, we can purify our existence in this human form of life. This Kṛṣṇa consciousness movement means to purify the existence, and after death, tyaktvā dehaṁ punar janma naiti (BG 4.9). If you become perfect in Kṛṣṇa consciousness, means you understand Kṛṣṇa... Janma karma ca me divyaṁ yo jānāti (BG 4.9). Simply by understanding and acting accordingly, you can purify your existence, and next life means after giving up this body... This body we have to give up. But those who are not purifying their existence, they will accept another material body. And those who have purified the existence, they will go back home, back to Godhead.