“Now therefore, I pray you, make a wager with my master the king of Assyria, and I will give you two thousand horses, if you are able for your part to set two thousand riders on them.”
Now he sought to emphasise Hezekiah's weakness by further derision. Let them simply compare the size of their cavalry. The verb ‘arab means ‘to pledge' and the hithpael ‘to pledge oneself', for example in a wager. The challenge was as to whether Hezekiah could produce two thousand capable horsemen. Then, if he succeeded in doing so, the king of Assyria would give them two thousand horses for them to mount. The purpose of the offered wager was in order to demonstrate both Judah's poverty with regard to capable manpower in that regard, and also in order to emphasise that they had few horses of their own. That they had no cavalry to speak of. In contrast Assyria for their part could easily spare two thousand horses, and not notice it. The emphasis is on how weak Hezekiah's cavalry were, comparatively a mere handful, in contrast with the huge Assyrian cavalry which all could see there, eagerly awaiting their opportunity. It was intended to weaken the resolve of the listening people on the wall.
The Rabshakeh's bad Hebrew, faithfully recorded here, is in fact smoothed out in 2 Kings, confirming that Isaiah is not a copy of that record.