John Calvin 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 come, give a hostage. He concludes that there will be nothing better for Hezekiah than to set aside the intention of carrying on war, to surrender himself, and to promise constant obedience to the king of Assyria.

To persuade him further, Rabshakeh again reproaches him with his poverty. “If I give you two thousand horses, you will not find among all your people men to ride on them. What then is your strength; or with what confidence do you dare to oppose my king?” He does not offer him horses for the sake of respect or kindness, but in order to terrify and shake even more the heart of Hezekiah.

The future tense should therefore be explained by the subjunctive mood, “Although I give you two thousand horses, yet you will not find an equal number of riders.” I am aware of what is alleged by other commentators; but whoever examines the matter fully will quickly perceive that this is ironical language.