In plain words
Karma alone was the cause of so many dying in the Kurukṣetra war and of the Pāṇḍavas and Kauravas fighting it. Once Dharmaja questioned Kṛṣṇa: ‘Kṛṣṇa! Why did You bring about so great a war for the sake of this paltry rule over a kingdom? Forty lakh soldiers have died in this war. But what falls to the Pāṇḍavas from it is one thing only! That is, the kingdom. To take forty lakh lives for the sake of these five Pāṇḍavas: is that just in any way?’ So he spoke. Then Kṛṣṇa: “You foolish fellow! You are looking at Quantity, but I look at Quality. Understand this inner meaning well,” he said. How many dogs would it take to equal one lion? This Kurukṣetra is the body. ‘Kuru’ means work. This body is a machine that does work. It is the basin in which karmas grow. So they called this body Kurukṣetra. In such a body bad qualities kept growing. Here is a fine example of it.
“A carbuncle rose on a man's back. Little by little it grew and threatened to spread over the whole body. If it comes on a hand, you can cut the hand off. If it comes on a leg, you can cut the leg.