yadā — when; saṁharate — winds up; ca — also; ayam — he; kūrmaḥ — tortoise; aṅgāni — limbs; iva — like; sarvaśaḥ — altogether; indriyāṇi — senses; indriya-arthebhyaḥ — from the sense objects; tasya — his; prajñā — consciousness; pratiṣṭhitā — fixed.

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.

The test of a yogī, devotee or self-realized soul is that he is able to control the senses according to his plan. Most people, however, are servants of the senses and are thus directed by the dictation of the senses. That is the answer to the question as to how the yogī is situated. The senses are compared to venomous serpents. They want to act very loosely and without restriction. The yogī, or the devotee, must be very strong to control the serpents – like a snake charmer. He never allows them to act independently. There are many injunctions in the revealed scriptures; some of them are do-not’s, and some of them are do’s. Unless one is able to follow the do’s and the do-not’s, restricting oneself from sense enjoyment, it is not possible to be firmly fixed in Kṛṣṇa consciousness. The best example, set herein, is the tortoise. The tortoise can at any moment wind up its senses and exhibit them again at any time for particular purposes. Similarly, the senses of the Kṛṣṇa conscious persons are used only for some particular purpose in the service of the Lord and are withdrawn otherwise. Arjuna is being taught here to use his senses for the service of the Lord, instead of for his own satisfaction. Keeping the senses always in the service of the Lord is the example set by the analogy of the tortoise, who keeps the senses within.

Seeing things with the material senses means being blinded to the spiritual reality. The world of sense, maya, is like a thick covering that clouds the soul. When your senses are attached to the objects of sense, it's like being led around by every cloud that passes across the face of the sky, and your spiritual awareness can't develop when you're constantly distracted by the objects of sense. It says in this verse that we should be able to voluntarily withdraw our senses from the things that appeal to them, like a tortoise can draw all its limbs into its shell. Now we all know that it can be difficult to impose this exile from the world of sense on ourselves, so Krsna has made it easy for us to replace our fascination with sense-objects with unalloyed devotional service by giving us the Hare Krishna mantra and the deity in the temple. The way to overcome our addiction to sense objects and appearances is to always be serving the Lord, and to always be taken up in the spontaneous love of the Godhead, which is the token of His grace.

So if you're struggling to overcome attachment to appearances, and it feels like you're missing the deeper reality, just remember that Krishna is the all-attractive Personality of Godhead, and He can satisfy your desire for spiritual enjoyment far more than anything He has created. Krishna is the supreme object of devotion, the goal of all sacrifice. Consider this famous statement of St. Augustine, from the first book of his Confessions: "You arouse us so that praising you may bring us joy, because you have made us and drawn us to yourself, and our heart is restless until it rests in you."