What is the Central idea of the poem "if"?

1.the hosts on two opposing mountains stood,  

2.thick as the foliage of the waving wood;  

3.between them an extensive valley lay,  

4.o'er which the gleaming armour pour'd the day,  

5.when from the camp of the philistine foes,

6. dreadful to view, a mighty warrior rose; in the dire deeds of bleeding battle skill'd,

the answer should be:

the intervention of the supernatural gives gilgamesh hope that he will defeat humbaba.