The few seconds they spent possessing her already took a few months away from her lifespan, so it is a good idea to choose an oracle that can last a long while.
They want a child that has been raised with their doctrine and is in perfect synchronization with them to be their next Oracle. This way the burden won't be so much and the new Oracle will last longer.
It will take a while to create such a child. In the meantime, they plan to take over every tribe around them. The first thing they have to do is gather information about the gods in their surroundings. The second most important thing is to eliminate those gods if they can.
That's why he went to the tribe nearby with two god seeds who haven't ascended yet. He discovered that one of the god seeds had been eliminated in the struggle. He had died, and since he hadn't ascended yet, he couldn't resurrect.
"Fighting before ascending is truly inefficient. But I guess they didn't have much of a choice."
