How sound is the saying: "Iraq is the skull of the Arabs, the treasure of faith, the substance of cities, and the spear of Allah on Earth, so rest assured, for the spear of Allah does not break," and what is its meaning?

This narration is not authentically attributed to 'Umar (may Allah be pleased with him), but its meaning is sound. "The skull of the Arabs" means their chiefs. "The treasure of faith" means its جمع (collection/source). "The spear of Allah" means that its people strive against the enemies of Islam and the people of innovation. "They protect their borders" means they guard the borders from enemies. "And they support the cities" means they provide Muslims with aid and strength.