C. F. Keil and Franz Delitzsch on Isaiah 13:2

Isa 13:2

The prophet hears a call to war. From whom it issues, and to whom or against whom it is directed, still remains a secret; but this only adds to the intensity.”On woodless mountain lift ye up a banner, call to them with loud sounding voice, shake the hand, that they may enter into gates of princes!” The summons is urgent: hence a threefold signal, viz., the banner-staff planted on a mountain “made bald” (nishpeh, from which comes shephi, which only occurs in Isaiah and Jeremiah), the voice raised high, and the shaking of the hand, denoting a violent beckoning - all three being favourite signs with Isaiah. The destination of this army is to enter into a city of princes (nedı̄bı̄m, freemen, nobles, princes, Psa 107:40, cf., Psa 113:8), namely, to enter as conquerors; for it is not the princes who invite them, but Jehovah.