Apparently these statements are contradictory, but because cow dung and conch shells are considered pure by the Vedas, they are accepted as pure by the followers of the Vedas, without argument. If we try to understand the statements by indirect interpretation, creating some hypothesis, then we challenge the evidential authority of the Vedic statements. In other words, Vedic statements cannot be accepted according to our imperfect interpretations; they must be accepted as they are. If they are not accepted in this way, there is no authority in the Vedic statements.
According to Lord Caitanya, those who try to give some personal interpretation to Vedic statements are not at all intelligent. They mislead their followers by inventing their own interpretations. In India there is a class of men known as Ārya-samājists, who say that they accept the original Vedas only and reject all other Vedic literature. The motive of these people, however, is to give their own interpretation. According to Lord Caitanya, such interpretations are not to be accepted. They are simply not Vedic. Lord Caitanya said that the Vedic statements of the Upaniṣads are like sunlight. Everything is clear and very distinct when it is seen in the sunlight; the statements of the Vedas are similarly clear and distinct. The Māyāvādī philosophers simply cover the sunlight with the cloud of their misinterpretation.