Albert Barnes Commentary Isaiah 36:8

"Now therefore, I pray thee, give pledges to my master the king of Assyria, and I will give thee two thousand horses, if thou be able on thy part to set riders upon them." — Isaiah 36:8 (ASV)

Now, therefore, give pledges – The margin says, ‘Hostages.’ The Hebrew verb (ערב ‛ ârāb) primarily means to mix or mingle; then, to exchange commodities by barter or traffic; then, to become surety for anyone, to exchange with him, to stand in his place; then, to pledge, to pledge one’s life, or to give security of any kind.

Here it is used in a spirit of taunting or derision, and is equivalent to what we might say, ‘I will bet you, or I will lay a wager, that if we were to give you only two thousand horses, you could not find enough men to ride them, or men with enough horsemanship knowledge to guide them.’

There was much severity in this taunt. The Jews hoped to defend themselves, yet an immense army was approaching to lay siege against them. What hope did they have of defense?

They were so weak and feeble that Rabshakeh said they could not furnish even two thousand horsemen to resist the entire Assyrian army. There was also, undoubtedly, much truth in this taunt.

It was not permitted by the Law of Moses for the Jews to keep cavalry, nor for their kings to multiply horses. The reason for this may be seen in the notes at Isaiah 2:7. Although some of the kings, especially Solomon, had disregarded this law of Moses, Hezekiah had endeavored to restore its observance. It is probable that he had no cavalry, and that the art of horsemanship was little known in Jerusalem.

Since the Assyrians prided themselves on their cavalry, they consequently looked with contempt on a people who were lacking this means of defense.