In plain words
Weapons do not cut It, fire does not burn It, water does not wet It, and wind does not dry It.
Word for word
Weapons do not cut this [one], fire does not burn this [one], and waters do not wet this [one], wind does not dry [it].
The commentators
Bhagavadgītābhāṣyam
कस्मात् अविक्रिय एवेति, आह —
एनं प्रकृतं देहिनं न च्छिन्दन्ति शस्त्राणि, निरवयवत्वात् न अवयवविभागं कुर्वन्ति । शस्त्राणि अस्यादीनि । तथा न एनं दहति पावकः, अग्निरपि न भस्मीकरोति । तथा न च एनं क्लेदयन्ति आपः । अपां हि सावयवस्य वस्तुनः आर्द्रीभावकरणेन अवयवविश्लेषापादने सामर्थ्यम् । तत् न निरवयवे आत्मनि सम्भवति । तथा स्नेहवत् द्रव्यं स्नेहशोषणेन नाशयति वायुः । एनं तु आत्मानं न शोषयति मारुतोऽपि ॥ २३ ॥
In plain words
Why changeless, and nothing but changeless? He answers —
A blade can't cut this Self, because there's nothing in it made of parts for a blade to pull apart. Fire can't burn it either -- there's nothing there to reduce to ash. Water can't soak it -- water only works by getting between the parts of something that has parts, and this has none. And wind can't dry it out the way it dries up something oily by evaporating the oil in it -- there's no moisture here to take. None of the elements can touch it, for the simple reason that it was never made of pieces to begin with.
Close to the Sanskrit
From what [reason is it] changeless only — thus [the question]; he says —
Weapons do not cut this aforementioned embodied one; because it is without parts, they do not effect a division of parts. 'Weapons' [means] sword and the like. Likewise fire does not burn this one; fire too does not reduce it to ashes. Likewise the waters do not moisten it. For water has the capacity, by producing a state of wetness, to bring about a separation of parts in a thing that has parts. That [capacity] is not possible in the partless Self. Likewise wind destroys an oily substance by drying up its oiliness. But even wind does not dry up this Self.