In Isaiah 36 an Assyrian advisor makes a fourfold case for Jerusalem to surrender. Three of these reasons are entirely correct; in the fourth the Assyrian erred greatly and quite possibly cost his country almost two hundred thousand men. In what follows I aim to analyze what was said and the effect it may have had upon God, upon Hezekiah and ultimately upon the Assyrians.
The message the ambassador brought had many components. However the opening question was: "What is the source of your confidence?" (Isa 36:4). The Assyrian then goes on to make four apparently devastating points:
That the first three of these arguments were true is revealed within the book of Isaiah itself:
Given the strength of these three arguments one wonders why the Assyrian introduced the fourth. In fact Isaiah 10:12 gives us the answer: pride. The Assyrian's had the pride to believe that they were doing this in their own strength. They also had plans beyond what God had allotted them . Therefore the advisor went beyond the statement of Biblical fact; and this led to their downfall.
Ironically it may even be the case that the Assyrian's words did not only provoke the ire of God but may also have provoked the behavior in Hezekiah that led to the saving of Jerusalem. It is noticeable in the passages in Isaiah 22 and 31 discussing military pride and trust in Egypt that on both occasions it stated that the people were not trusting in God. It could well be that when Hezekiah heard the message from the Assyrian that he performed the same analysis I just did and spotted that the one thing he hadn't really tried was faith in God.
It is noticeable that whilst all four of the arguments above were mentioned by the Assyrian it was the fourth that they chose to focus upon. Each of the others are mentioned but once. The 'error' of trusting in God was mentioned four times by the advisor. When Sennacherib then writes it is only the error of trusting in God that is mentioned. I suggest therefore that it is the Assyrian's that actually focus the Israeli mind upon the ultimate question: should they trust God?
There are some that would argue that the reaction of Hezekiah was immaterial: the Assyrian mistake was to anger God. However I would note that the eventual demise of the Assyrian and their arrogant hearts had already been dealt with in detail in the tenth chapter. God was not surprised by this exchange. However Hezekiah's prayerful response may not have surprised God but it was actionable.
Isa 37:21 Isaiah son of Amoz sent this message to Hezekiah: "This is what the LORD God of Israel says: 'Because you prayed to me concerning King Sennacherib of Assyria, (Bold mine)
We therefore see that the angel that destroyed the 185,000 men was in direct response to the prayer of Hezekiah. Remembering that the majority of Judah had already fallen by this point we must conclude that something new had provoked Hezekiah to trust in God rather than his own defenses or an Egyptian alliance. This new thing may well have been the arrogance of the Assyrian.
In conclusion we may notice the danger of the half-truth; or in this case the three quarter truth. The Assyrian's had been sent by God to attack a people that were trusting in strategy and alliance. This was enough reason for them to have won. Instead they chose to repeat the mistake the Israelis were making: they trusted in self and became prideful and arrogant. The result of this may well have been a spiritual revival on the part of the Jew and was certainly the physical destruction of a significant portion of the Assyrian army.