Krishna lays out a ladder of increasing subtlety. The physical body is gross. The senses are subtler and more powerful than the body. The mind is subtler and more powerful than the senses. The intellect surpasses the mind. And beyond even the intellect stands the Atman — the Self.
This hierarchy matters because desire nests at every level. To defeat it, you must climb higher than where it hides. If it sits in the senses, use the mind. If it invades the mind, use the intellect. If it taints even the intellect, only the Self — the awareness behind everything — can see through it. The ladder points you toward the ultimate vantage point.