A brāhmaṇa is . . . he has got his duties, to practice how to become truthful, satya; śama, how to control the senses; and dama, how to control the mind. Satyaṁ śamo damas titikṣā, how to learn toleration, forbearance. Satyaṁ śamo damas titikṣā, ārjavam, how to become simple, not crooked. Jñānam, full knowledge in everything. Vijñānam, practical application. Satyaṁ śamo damas titikṣā ārjavaṁ jñānaṁ vijñānam āstikyam (BG 18.42), full faith in the Vedic literature. That is called āstikyam. That is called theism, to believe in the śāstras without any deviation. That is called theism. Atheism means not to believe in the śāstra or not to accept them as it is, to comment according to one's own whim. That is called atheism. Theism means to have faith, full faith in the Vedic knowledge. That is called theism.
That I have given you several times the example: Just like the cow dung is the stool of an animal, but the Vedic literature confirms that cow dung is pure. Now, you cannot argue, "It is stool of an animal. In one place you have condemned that if you touch the stool of an animal, you have to take bath thrice, and now you say cow dung, which is also stool of an animal, it is pure. Where is your argument?" You have to accept. That is called theism. Because the Vedas says, without any argument you accept it. That is called theism. You cannot change. You cannot comment. That is called theism. Āstikyam. Brahma-karma svabhāva-jam (BG 18.42). And unless you have got such faith in the Vedic knowledge, you cannot make any progress. That is not possible. If you, with your poor fund of knowledge, you want to interpret, from the very beginning there is no question of progress.