In short, the 5 month defense that began with the Japanese attack in December, although eventually overrun, was enough to disturb the invaders' Pacific War timetable, giving the Allies the time to organize and prepare counteroffensive measures that started to push Japanese conquests back in mid-1942. I'll also mention that although MacArthur received the Medal of Honor, he himself recognized that the American and especially (inadequately trained and supplied) Filipino troops (who made up 85% of the force) deserved the most credit. To quote MacArthur: “This award was intended not so much for me personally as it is a recognition of the indomitable courage of the gallant army which it was my honor to command.”
To provide more detail, MacArthur made some important decisions that served to delay the Japanese invasion including:
realizing early on that defeating the Japanese was highly unlikely, he modified the mission of the United States Army Forces in the Far East to delay the victory rather than defeat the invasion which involved the implementation of "War Plan Orange 3" which is the organized withdrawal to and defense of the Bataan Peninsula.
the Japanese tried to win this "race to Bataan" by cutting off and destroying the USAFFE by sending two invasion forces (one from Manila area and the other from the Lingayen Gulf), so MacArthur set up 5 lines of defense in a phased withdrawal that was successful at winning this "race" (thanks to the work of I Corps under Major General Jonathan M. Wainwright and II Corps under Major General Edward P. King) by providing an effective roadblock to the Japanese invasion despite terrible conditions, shortages of food and ammo, disease and heavy casualties, while meanwhile tasking Brigadier General George M. Parker Jr. with the task of setting up defensive positions of Bataan and stocking it with enough food, water and supplies. An amazing 80,000 troops were able to make it to defensive positions on Bataan. By wisely delegating control of the fighting to Wainwright and King, he understood the importance of small unit tactical fighting.