Bhagavad Gita: Chapter 2/Verse 17

अविनाशि तु तद्विद्धि येन सर्वमिदं ततम् ।
विनाशमव्ययस्यास्य न कश्चित्कर्तुमर्हति ॥२- १७॥

avināśi tu tadviddhi yena sarvamidaṃ tatam ।
vināśamavyayasyāsya na kaścitkartumarhati ॥2- 17॥

But you should know that indestructible by which all this is spread out. No one is capable to carry out the destruction of this imperishable. 
 
Word-for-word translation

avināśi (nominative, singular) = indestructible 

tu (conjunction) (indeclinable) = but

tat (pronoun, 3rd person, nominative, singular) = that 

viddhi (imperative, 2nd person, singular) = you should know

yena (pronoun, 3rd person, instrumental, singular) = by which

sarvam (accusative, singular) = all

idam (accusative, singular) = this

tatam (past passive participle) = spread out


vināśam (accusative, singular) = destruction 

avyayasya (genitive, singular) = of the immutable

asya (pronoun, genitive, singular) = of this

na (adverb) (indeclinable) = not

kaścit (indefinite article) = one

kartum (infinitive) (indeclinable) = to carry out

arhati (present tense, 3rd person, singular) = one is capable


Commentary

The translation of this verse is very choppy in English given the Sanskrit words in this verse are very abstract and difficult to relay in English with the Sanskrit syntax as it is. Like other translations, I decided to be true to the Sanskrit literal meaning, but below I will paraphrase what the verse is relaying:

You should know that substance in nature that is indestructible from which everything in nature comes from. That substance is not capable of being destroyed by anyone because of its imperishable nature. 

This is a very important philosophical concept in the Bhagavad Gita. It is saying that there is something in nature that is outside of time, but from which everything subject to time comes from. It always was and will always be.