Now Arjuna comes in action.  

             Bg 1.20

atha vyavasthitān dṛṣṭvā
dhārtarāṣṭrān kapi-dhvaja
pravtte śastra-sampāte
dhanur udyamya pāṇḍava
hṛṣīkeśa tadā vākyam
idam āha mahī-pate

Word for word: 

atha — thereupon; vyavasthitān — situated; dṛṣṭvā — looking upon; dhārtarāṣṭrān — the sons of Dhtarāṣṭra;kapi-dhvaja — he whose ag was marked with Hanumān; pravtte — while about to engage; śastra-sampāte — in releasing his arrows; dhanu — bow; udyamya — taking up; pāṇḍava — the son of Pāṇḍu (Arjuna); hṛṣīkeśam— unto Lord Kṛṣṇa; tadā — at that time; vākyam — words; idam — these; āha — said; mahī-pate — O King.

Translation: 

At that time Arjuna, the son of Pāṇḍu, seated in the chariot bearing the ag marked with Hanumān, took up his bow and prepared to shoot his arrows. O King, after looking at the sons of Dhtarāṣṭra drawn in military array, Arjuna then spoke to Lord Kṛṣṇa these words.

atha vyavasthitān dṛṣṭvā, as they are situated they observed ,

dhārtarāṣṭrān, the army of Dhritarashtra was arranged. He saw them, who saw them? That person who was kapi-dhvaja, dhvaja refers to flag, kapi means monkey. Later on in Mahabharata it is stated that when Kaurava would look at Arjuna's chariot they will feel that there is monkey on the flag and the monkey is real and screaming, the monkey is causing terror in the heart of enemies of Arjuna, they would think what is this? Every warrior would have his flag by which other warriors would recognize him that is the standard. Arjuna always was having kapi-dhvaja flag but in this war on the request of Bhima Hanuman Ji had entered in that flag that is the reason the flag which was just supposed to be a flag was alive and Kauravas were horrified by seeing that.

When Pandavas were in forest, Arjuna went to heaven to collect weapons and mystic powers that time Bhima went more north from Badrikashram there he met a monkey who humbled him and he was Hanuman Ji. Both of them were brother as being sons of Vayu… So in this way Arjuna magnificent chariot Mahti Sandana is having kapi-dhvaja, this is sign of auspiciousness and victory.

pravtte śastra-sampāte, they are all equipped with weapons.

dhanur udyamya pāṇḍava, that means Arjuna has taken up this bow, and he was ready to fight.

Then what did happened?

hṛṣīkeśa tadā vākyam, at that time he spoke to Hṛṣīkeśa.

What did he speak? idam āha mahī-pate, so here mahī-pate refers to O’ King, this Sanjay is speaking to Dhritarashtra O’ King this is what to Rishikesh pandava (Arjuna) spoke