Map of Pacific
From National Geographic

The Japanese Imperial Navy had believed that the U.S. Fleet would attack the empire from the southeast, toward the triangle conecting Port Moresby, Tulagi, and Rabaul. If the Japanese would be able to launch regular air searches in the south Coral Sea, they would have suitable time to hinder any Allied naval approach. Taking Port Moresby would also allow the Japanese to launch land based raids against airfields in northern Australia in the hopes of neutralizing them. The Japanese would then avoid an air battle of attrition over their own bases because Port Moresby was out of range for Allied fighters based in Australia. Port Moresby also provided a link to the Netherlands East Indies, allowing a direct staging of bombers along the whole length of their defensive perimeter. The importance to the Japanese for taking Port Moresby was twofold. It would deny the Allies a strategic position in which they could start an offensive against Japan, and it could be utilized as an air base protecting the perimeter of Japanese holdings in the Pacific.

After Admiral Isoruku Inoue had assessed his losses in the Battle of the Coral Sea, he still considered the invasion of Port Moresby. Inoue felt that one weakened carrier air group, Zuikaku, was not enough to support the invasion convoy against Allied land-based aircraft stationed in Australia. Also, the MO Striking Force could not provide support without a couple day delay. The remnants of the MO Striking Force would have to regroup and refuel before it could be involved in any action.

The Battle of the Coral Sea was significant because it stopped the advance of the Japanese on Port Moresby. Even though Port Moresby had suffered bombing raids by Japanese forces, it was never in danger of being captured. For the duration of the war, the Japanese never again threatened Port Moresby nor the entire island of New Guinea.