|Chapter 2: Contents of the Gita Summarized|
yada samharate cayam
kurmo 'nganiva sarvasah
tasya prajna pratishthita
One who is able to withdraw his senses from sense objects, as the tortoise draws its limbs within the shell, is firmly fixed in perfect consciousness.
In the next 6 verses (2.58-2.63) Krishna responds to Arjuna's third question, "How does he sit?" which means, how does a transcendentally situated person control his senses?
Krishna here uses the analogy of the tortoise to explain the position of such a person. A tortoise at its own free will can withdraw its limbs and when needed manifest them. Similarly a "stitha-pranja" is one who has willful control of the senses. Srila Prabhupada explains that the senses are like venomous serpents that left unchecked have the ability to do enormous harm. Most of the people are "go-das" which means that they are the servant of their senses. A transcendalist aspires to become a "go-swami" or master of the senses.
An important point to note here is that Krishna does not recommend that the senses are discarded or denied. He recommends control. The nature of this control is described in the next verse.
Please read the Sanskrit Verse and the Prabhupada's Purport.