The rules laid down by the author of the Nirukta apply to every part of the Vedas. All the mantras treat of three classes of subjects.
Some of them treat of Paroksha (not sense-cognized), some of Pratyaksha (sense-cognized) and others of Adhyatmika subjects (pertaining to the self).
In mantras belonging to the first category the third person is used, in the second, the second and in the third, the first. But there are two rules for the use of the second person, viz. that the second person is used when inanimate objects are Pratyaksha.
The purpose is to treat inanimate objects as Pratyaksha for the sake of emphasizing their utility. Not knowing this rule the Vedic commentators Sayana and others and their followers the European scholars who have translated the Vedas in their own tongues misinterpreted them as sanctioning the worship of inanimate objects, Nirukta. VII. I & 2.