"but it is as if we have only given birth to air" or "it is like we gave birth to nothing." This is a simile that emphasizes that the people's suffering resulted in nothing. Alternate translation: "but nothing good resulted from it" (See: [[rc://en/ta/man/translate/figs-simile]])
Here "earth" represents the people who live on the earth. The meaning is unclear, but it seems to mean that the people of Israel have not been able to save themselves or other people by defeating their enemy in battle. (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-explicit]])
This can be reworded so that the abstract noun "salvation" is expressed as the verb "save." Alternate translation: "We have not saved the inhabitants of the earth" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])