Krishna says (2.58) that wisdom gets established when one completely withdraws their indriyas (senses) from sense objects, like the tortoise withdrawing its limbs.
Krishna lays emphasis on indriyas as they are the gateways between our inner self and outer world. He advises that we should withdraw our indriyas when we see ourselves getting attached to sense objects like the metaphorical tortoise withdrawing its limbs when faced with danger.
Each sense has two parts. One is the sense instrument like an eyeball and the second, that portion of the brain (controller) which controls this eyeball.
Sensory interactions happen at two levels. One is between the ever changing outer world of sense objects and the sense instrument (eyeball) which ispurely automatic where photons reach the eyeball and interact as per their physical properties. The second is between the eyeball and its controller.
The desire to see is the reason for the evolution of the eye and that desire is still present in the controller part of the sense. This is known as motivated perception where we see what we want to see and hear what we want to hear. In a game of cricket, we tend to notice more decisions favouring the opposition and conclude that the umpire is unfair.
When Krishna refers to Indriya, he is speaking about the controller part which generates the desire to sense. That's why even when we shut our senses physically, the mind uses its power of imagination to keep our desires alive - the mind being the combination of all these controllers.
Krishna is guiding us through this scientific verse to separate the controller from the physical part of the senses so that we attain ultimate freedom (moksha) from the ever exciting or depressing external situations. Wisdom is to know when to withdraw from a situation.
Source - Daily World