Learning new knowledge can boost spirit energy?
It sounds a bit far-fetched, but in fact, it's not that implausible.
For the Chosen Ones, to enhance their spirit energy, all they need is to drink more Elemental Potions and then just lie down and sleep—their spirit energy strength and development will grow with age, as if they already possess the final form of spirit energy, and simply need time to break the seals.
Many people in the Terra Continent believe that Chosen Ones are actually the reincarnations of those powerful spirit energy users from the past. Their memories might have been erased by the Nether Sea, or say, within the natural spiritual energy fields between heaven and earth, but a portion of their mighty spirit energy can still be preserved, helping themselves set foot on the path of spirit energy once again in their next lives.
Considering Ian himself is also a reincarnation, he thinks this possibility is quite significant.