Bhagavad Gita Verse 25, Chapter 2

avyaktoyamachintoyamavikaryoyamuchyate |
tasmaadevam viditvainam naanushochitumarhasi || 25 ||
 
This (eternal essence) is imperceptible, this is incomprehensible, this is unchanging, it is said. Therefore, having known this, it is not worthy of grief.
 
avyaktaha : imperceptible
ayam : this
achintaha : incomprehensible
avikaryaha : unchanging
uchyate : it is said
tasmaad : therefore
evam : thus
viditva : having known
enam : this
naa : not
anushochitum : grieve
arhasi : worthy
 
Let's take stock of where we are. In the second chapter, Shri Krishna covers 4 main topics: 1) Informing Arjuna that his logic and reasoning was incorrect 2) Explaining the correct logic and reasoning to Arjuna 3) Providing practical guidance to implement this correct logic and reasoning 4) Describing the attributes of a person who follows this teaching.
 
We are still exploring the second topic, and this shloka marks the end of the argument that Shri Krishna began in shloka 17. The argument was whether the eternal essence can slay or be slain. Shri Krishna, in this shloka, concludes the argument by saying the following:
 
"Arjuna, associate yourself with the eternal essence and not the body. The eternal essence is eternal and imperishable; it cannot slay or be slain. Therefore do not grieve for the opposing army's warriors on their imminent death. Their bodies will perish anyway, so you shouldn't grieve for what is bound to perish. The eternal essence which is common between them and you is imperishable, so you should not grieve for that either. Therefore you have no reason to grieve at all."
 
Let's look further. If something is imperceptible, that means it is beyond the realm of our sense organs. If something is incomprehensible, it is beyond the realm of the intellect. If something is unchanging, then no physical effort will have an impact on it. We are dealing with something that is not of this material world, it is beyond it.
 
In the next few shlokas, Shri Krishna provides a simpler alternative of logic and reason to Arjuna, after which the teaching takes a turn towards more practical and concrete topics.