This operation (the battle for the island of Guadalcanal) was hugely important. If it had not succeeded, it would have been very hard for the United States to win the war in the Pacific.
If the Japanese had taken Guadalcanal, they would have been able to cut off the shipping lanes to Australia. They might eventually have been able to invade Australia itself.
If they had cut off the shipping lanes, the US could not have used Australia as a base from which to launch its attack northward towards Japan. All US movements would have had to originate from Hawaii and go through Japanese-held Micronesia. Those islands would have been better defended as well because Japan would not have had to worry about attack from the south.