rjun says, "The hosts of gods surrender unto you. Filled with fear, some praise you with folded hands (11.21). The 𝙍𝙪𝙙𝙧𝙖𝙨, 𝘼𝙙𝙞𝙩𝙮𝙖𝙨 etc. behold you quite astonished (11.22). Seeing your mighty form with many mouths and eyes, many arms, thighs and feet, many stomachs, many terrible tusks, the worlds are terrified, so am I (11.23). Seeing you touching the sky, my mind is terrified and I find no courage or peace (11.24). Seeing your mouths with terrible tusks and fires, I lost sense of directions" (11.25).
Arjun says that Gods are filled with fear and worlds are terrified. Fear and favour (expectation) form a set of polarities. Hence, behind a favour, fear is hidden. Favour could be from 𝙋𝙖𝙧𝙖𝙢𝙖𝙩𝙢𝙖, family, boss or even from ourselves. Fear is born when we apprehend that favour wouldn't be bestowed. When favour seeking is dropped, fear automatically disappears. Gods too are seeking favours from 𝙑𝙞𝙨𝙝𝙬𝙖𝙧𝙤𝙤𝙥𝙖𝙢 of Krishna for themselves or their devotees and hence their fear is bound to follow that.
A flowing river is the best example to understand the host of dualities or polarities Arjun finds in 𝙑𝙞𝙨𝙝𝙬𝙖𝙧𝙤𝙤𝙥𝙖𝙢. A river has two banks and both of them merge as riverbed. A River can't flow with one bank. It invariably needs two banks who are exerting pressure in opposite directions. On the other hand, if these banks don't meet at the riverbed, then it would be an infinitely deep valley and a river can't exist. Our senses can't penetrate water and hence can't perceive the riverbed. They can't even see the opposite bank when the river is mighty. Similarly, we too miss other pair of polarity in this mighty existence. Likewise, we have the manifested world which is invariably polar (river banks) and these polarities unite at the un-manifested (riverbed) and that's what Arjun is seeing in 𝙑𝙞𝙨𝙝𝙬𝙖𝙧𝙤𝙤𝙥𝙖𝙢.