The essence of the battle of Karna and Arjuna in Mahabharata, what did Lord Krishna say to Arjuna after seeing Karna?

 When the final and decisive war of Mahabharata was taking place between Karna and Arjuna. So this war was so destructive, as if Shakasat Neel Kand Mahadev i.e. Lord Shankar is fighting the war on the pretext of war. That is, Yama Raj, the god of death, is fighting a war.

 

Arjun and Karna  war

What did Krishna say to Arjuna and Karna?

In this disastrous war, Lord Krishna says by giving Karna's courage and might, that you are blessed Karna, such a war is born no one before now. And maybe someone will be born in the coming age. Because Karna pushed Arjuna's chariot back by a step. Arjuna pushed Karna's chariot seven steps back.

Arjuna says to Lord Krishna-

Hey! In Keshav, I have pushed Karna's chariot seven steps back and Karna has given my chariot only one step back, yet why are you praising Karna.

Lord Krishna says that-

Hey! Partha Karna is again Karna. At the present time, there is no war beyond this. I believe that you have shifted Karna's chariot seven steps back. But still there is a greater war Karna than you. Hearing this talk of Lord Krishna, Arjuna starts to move away.

Tell me, why is Karna a bigger war than me? - Arjun

Lord Krishna tells Arjuna that hey! The chariot you are on is the chariot that is tied to the Hades by the Sethnag itself, and I myself am sitting on this chariot carrying the weight of all the three locos, Mahabali Hanuman is seated on your chariot and protecting this chariot. If the chariot is still pushing your chariot backward, then it is not an ordinary war, Partha! If your chariot went back and forth a little bit, then my place would have become empty, otherwise I would have had to leave the tiloka. 

Lord Krishna tells Arjuna that hey! Partha today if you take your dhandiv and wear your Sudarshan Chakar in it, we both fight with Karna. Even today Karna will probably lose from us.