God is represented as a warrior who is preparing himself to shoot arrows at the Babylonians. They are not literal arrows but symbolize him directing his wrath against them. Since they are the objects of his wrath, he uses the arrows as his weapon to fire his vengeance upon them. He called for many arrows which referred to him equipping himself to launch into an attack against them. His arsenal of arrows which fills the sheath will be directed toward them to bring about their destruction.
The words, you split the earth with rivers
suggests that his attack upon them will be swift and sudden. It will be like a heavy downpour of rain falling upon the earth. This deluge of water would result in his people being avenged for the suffering they endured at the hand of the Babylonians.
9 You stripped the sheath from your bow, calling for many arrows. Selah You split the earth with rivers.