It's perfectly fine to call lightning - the second mother.
Being caressed by this lightning, everyone including Xue Ren and Di Xun felt estatic. Their bodies were getting tempered by it and even their souls got the best treatment.
At the times when the demons advance everywhere they can, tempering soul is important. Soul concept might be hard, but at least soul can be defended against hell's energy.
This hell's energy is both alive and soul energy. The mixture of it is similar to Superbia's sins energy and that's what makes demons scary. However, it doesn't really help Xue Ren much as he wants to grasp the concept of soul more thoroughly.
Even when he uses his dark violet energy, he mostly focuses on the alive concept, so he himself is far away from Rushai's level.
Then, the fifth throne comes with help.