The King of Assyria compares Egypt to a weak walking stick; you expect that it will support you when you lean on it, but instead it breaks and cuts you. Alternate translation: "the weak support from Egypt" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The speaker is extending the metaphor by describing what happens when a reed is used as a support. Alternate translation: "but if someone uses this for support, he will be injured" (See: [[rc://en/ta/man/translate/figs-metaphor]])