The words uttered by the Nine Deadly Poison Devil had given Su Yu some understanding of his own Holy Decree. When he joined hands with Xia Jingyu, it could bring out the power of a saint grade Holy Decree. So, if he were to make his move alone, the Holy Decree should only be half the saint grade level.
While his old Holy Decree was undergoing a transformation, his new Holy Decree had not yet formed. So there was only half the Holy Level. Su Yu wasn't sure if he was entirely correct with his newfound understanding, but he was going to have to give his theory a shot! In Su Yu's mind, there already was a concept of a Holy Decree. Now, in his strong hands, he had formed a newly-improved Holy Decree!