The answer is: It encourages Gilgamesh to fight and adds excitement for the audience.
In the following excerpt we can find Lord Shamash's intervention, here he is encouraging Gilgamesh to fight adding emotion and fervor to the adventure.
“Then, from heaven, the voice of the god
called to Gilgamesh: "Hurry, attack,
attack Humbaba while the time is right,
before he enters the depths of the forest,
before he can hide there and wrap himself
in his seven auras with their paralyzing glare.
He is wearing just one now. Attack him! Now!"
