To break the Mist Barrier of Efanso, it would require at least half of Raymond's current Professional Level of Law Magic Power. If it's insufficient for the current Professional Level, he would suffer a Negative Rank, losing all the benefits obtained at that level, until he regained the missing portion of Law Magic Power.
Thus, it is one of the least used Spells by Mages, especially for a Quasi-Legendary Mage like Raymond, who was at a critical juncture of assaulting the status of Legendary Mage. Each use would severely delay his advancement into legend.
If Gaven hadn't offered a sufficiently generous price, Raymond would never have agreed to make a move.
"Arms of Efanso has been impersonated by an Akechazha Evil Beast Spirit, the longer we delay, the more danger the citizens of Efanso face. What's a loss of a million compared to the lives of tens of thousands?" Gaven spoke passionately, having already committed to the act, he naturally wanted to gild himself with glory.