By possessing Reverend San Le with a celestial fiend puppet and occupying An He City, Wu Qi's intention was to get himself a safe place where he could cure himself, while taking the opportunity to loot a batch of Pangu Continent's local products. This was the primeval land opened up by the Great Saint Pangu, where a full array of resources was available. Those outer heavenly realms could just not compare with it.
On top of that, Wu Qi also wished to get his hand on a current map of the Pangu Continent!
Yes, a map!