What is that explosion

Sitting under the waterfall, Wang had some ideas based on the records in the spear manual and wanted to explore them. His body was indeed benefiting from this but he had yet to accomplish his goal, over the years of fighting everywhere he had accumulated strong killing intent and spear force, that seemed to be always around his body, He wanted to use his willpower to compress the spear force completely until it underwent qualitative leap, but this was not easy to achieve as it had more than just sitting there and letting water whip at his body.