The śāstra says, striyaḥ sūnā pāna dyūta yatra pāpaś catur-vidhaḥ (SB 1.17.38). These four things are the four pillars of sinful life.
What are these? Avaida stri-saṅga: womanly connection which is illegitimate. You cannot have any connection with woman without being married. That is Vedic instruction. Otherwise, what is the difference between animal and man? There is no marriage in the animal kingdom. But in the human society, never mind whether it is in India or Russia or China, there is marriage system in the human society, maybe methods may be different. Therefore, womanly connection, man and woman living together without marital connection, that is pāpa, sinful life. That is the injunction of the śāstra.
Similarly, striyaḥ sūnā. Sūnā means unnecessarily killing the animals. Just like slaughterhouse. You cannot maintain slaughterhouse in the human society and at the same time you want peace. It is not possible. Every living entity is son of God. You cannot kill even an ant, then you dissatisfy God. Take for example just like a gentleman has got five sons, one of them is useless, doing nothing. But if the expert son says, "My dear father, your this son is useless. Let us kill him and eat," cannibal, will the father agree, "Oh, yes, yes, this son is useless. You can kill and eat"?
Time will come in this Kali-yuga when actually people will become what is called man-eater. Still there are existence man-eaters in Africa. So the human society is coming to that position. Like animal, they will eat their own sons and daughters. So therefore this practice, unnecessarily killing animal, is one of the pillar of sinful life.
Striyaḥ sūnā pāna dyūta. Pāna means intoxication. We are already intoxicated by illusion. Because we are in the material world, we are accepting false things. Just like this body. I am accepting I am this body. This is intoxication. I am soul, I am Brahman, but I am accepting this body that I am this body. This is already intoxication. And if you increase more intoxication, then where is the possibility of getting real knowledge, brahma-jñāna?
So the pāna, intoxication, should be avoided. Animal killing should be avoided. Illicit connection with woman should be avoided. And gambling, speculation, patavad(?), that should be eliminated, avoided. Then you get the chance of becoming pure. And without being pure, you cannot be engaged in the loving service of the Lord. The Lord is pure. Paraṁ brahma paraṁ dhāma pavitraṁ paramaṁ bhavān (BG 10.12). So you cannot approach Lord being impure. Even I do not indulge in illicit sex life or meat-eating or very much moralist, still I am impure if I think myself "I am Indian," "I am American," "I am Hindu," "I am Muslim." These are also impurities.
So the bhāgavat-dharma means to become completely pure. Sarvopādhi-vinirmuktaṁ tat-paratvena nirmalam (CC Madhya 19.170). And you cannot keep your purity without being in touch with Kṛṣṇa.