'Be Careful' in the Bible

Tell him, 'Be careful, and keep calm. Don't be afraid, neither let your heart be faint because of these two tails of smoking torches, for the fierce anger of Rezin and Syria, and of the son of Remaliah.

Be careful not to let Hezekiah mislead you when he says, "The LORD will save us." Has any god of any nation ever delivered his country from the king of Assyria?