Then, seeing the sons of Dhṛtarāṣṭra arrayed in order of battle, the Pāṇḍava whose banner bears the monkey, at the moment when weapons began to be discharged, raising his bow, spoke these words to Hṛṣīkeśa, oh lord of the earth

The decisive moment: atha (then) marks a fundamental change. The two armies are vyavasthitān (arrayed in formation), and śastra-sampātaḥ pravṛtte (the discharge of weapons has commenced) — violence is imminent.

Kapi-dhvajaḥ (of monkey-banner) is Arjuna, whose standard bears the image of Hanumān, symbol of devotion and strength. The monkey on the banner represents his domesticated mind serving dharma. That he speaks now, at the precise instant before the clash, is significant: his bow udyamya (raised, drawn) is ready, but his mind already wavers.

This is Sañjaya’s last intervention before Arjuna speaks directly for 42 verses.