Facing the looming military threat of the King of Assyria, the people receive a profound message of encouragement rooted entirely in faith in God's supreme power. The directive to maintain strength and courage echoes the familiar charge given to the nation early in the Book of Joshua [מלבי״ם]. Alongside this call for bravery is a strict warning against giving in to fear, panic, or a sense of brokenness when confronting the enemy.
The King of Assyria approaches with a massive, intimidating army, boasting both overwhelming numbers and immense physical power. Yet, the people are reassured that the force standing alongside them is far greater and stronger than anyone supporting the enemy. [מלבי״ם] explains that the nation possesses a superior strength simply because God is with them. His presence is meant to actively help the people when they engage in combat, and He is even prepared to fight their battles Himself, ultimately creating a situation where the people will not need to fight at all.