The senses, mind and intelligence are the seat of desire. Through these, it deludes the embodied soul, by veiling wisdom.
To deal with and sublimate strong passion and prejudice, a closer understanding about how they sprout and grow is necessary. That is why Krishna explains the presence and activation of passion in our personality.
Our body is inert and cannot act by itself. The same applies to the organs of knowledge and action. Therefore, the inner personality has to activate these with a touch of sentience. Mind, intelligence and ego constitute the inner personality.
Kāma, passion, lies coiled up in the senses, mind and intelligence, making it hard to reach and subdue it effectively. A physical entity can be easily approached and dealt with; but the inner factors are not so.
Interactional life penetrates from the sensory level inward, involving mind and intelligence. Passion and hatred enfold these, making it hard to tame and remove them. Krishna first points this aspect of kāma, passion.