This speaks about people relying on their horses to help them as if they were leaning on their horses. AT: "rely on their horses" (See: [[rc://en/ta/man/translate/figs-metaphor]])
The phrase "retract his words" speaks of a person not fulfilling what they said they will do as if the words that he had said were something that he could pull back to himself. Here it says that Yahweh will not do this, meaning he will fulfill what he has said. AT: "he will do what he said he would do" (See: [[rc://en/ta/man/translate/figs-metaphor]])