Why was it important that Israel was recognized by the United States and other nations?

It meant that other nations would supply Israel with economic aid
It meant that other nations agreed to trade with Israel
It meant that other nations would treat Israel as a legitimate state
It meant that other nations pledge to defend Israel in case of an attack

All of the above are correct. Recognizing Israel as a legitimate state signaled support for its existence and security, as well as opening up opportunities for economic aid, trade, and defense cooperation. This recognition helped establish Israel as a sovereign nation on the world stage.