Who actually reaches that supreme state? Krishna lists five qualities. First: freedom from pride and delusion. Second: having overcome the pull of unhealthy associations. Third: constant attention to the inner self. Fourth: desires that have naturally fallen away. Fifth: freedom from the tug-of-war between pleasure and pain.
These qualities do not arrive overnight. They ripen slowly, like fruit on a tree. A farmer who stays focused on his field through rain and heat is not bothered by the weather. In the same way, a person established in these qualities remains steady through life's highs and lows.
Krishna is not issuing a command here. He is describing a reality. Those who carry these qualities reach the imperishable state. It is a description, not a prescription.