How to realize Kṛṣṇa? In the every step of life you can realize God, provided you practice it. That is called bhakti-yoga, that is called Kṛṣṇa consciousness. Just like Kṛṣṇa says that raso 'ham apsu kaunteya (BG 7.8), "I am the taste of the water." So everyone drinks water and feels satisfaction. When he is thirsty and he drinks water, he becomes satisfied with the taste of the water. So Kṛṣṇa says: "I am the taste." So how one can say that, "I do not know God. I have not seen God. I have no experience of God"? God says: "Here is, I am."
Similarly, He says that prabhāsmi śaśi-sūryayoḥ (BG 7.8): "I am the shining of the sun, of the moon." So who has not seen the shining of the sun or the moon? Everyone has seen. So how do they say that, "Can you show me God?" Why don't you see God here? Why don't you see God in the taste of water? Why don't you see God in the sun shining. Why don't you see God in moonshine? Similarly, Kṛṣṇa says, dharmāviruddho kāmo 'smi (BG 7.11): the lust, in the lust desire, there is also God. So what is that? What kind of lust? Dharmāviruddho: which is not against religious principles.
So this sex life is not denied, because eating, sleeping, mating and defending, that is the necessity of the body. You cannot stop it. So there is concession that you can have sex life only for begetting children—for no other purpose. If you use sex life for any other purpose, that is against religious principles. There are other rules and regulations—that you can have sex with your wife five days after menstrual period, and if she is pregnant, then you cannot have sex life. So if you have sex life more than this, that is against religious principles. And if you become against religious principles, then you become sinful. And if you become sinful, then you cannot make progress towards God-realization.
Because sinful man cannot make progress in God-realization. As it is stated in the Bhagavad-gītā, yeṣāṁ tv anta-gataṁ pāpaṁ (BG 7.28). One who has finished his business in sinful activities, janānāṁ puṇya-karmaṇām—that simply they are engaged in pious activities—such persons, dvandva-moha-nirmuktā, becomes delivered from all dualities, and dvandva-moha, bhajante māṁ dṛḍha-vratāḥ, then become perfect devotee.