First of all, he had become able to speak properly. This was a surprisingly important thing, because by being able to speak words, he was finally able to chant the spells he was casting.
Up until now, he had been unable to chant the spells, and had been forcibly activating them by using an absurd amount of Mana. Therefore, each spell used Mana several times more Mana than it normally would and its potency was less than half of what it would normally be. If he hadn’t possessed such an abnormally huge amount of Mana, he would not have been to come as far as he did.

However, since he did come this far without reciting the spells at all, as soon as he was able to speak, he gained the【Chant Revocation】skill, which allowed him to cast spells without chanting them.