Chapter 633 - Decoding the Symbol
Inside the interrogation room, Philip fully concentrates on the symbol that appears on the left shoulder of that Abyss human. To reverse that symbol he needed to understand the whole mechanism of the symbol and how many layers are present in the symbol.
Not only that he also needed to understand what type of word was used to create those symbols. All this time he was using his spiritual vision technique that helped him to understand the details of these kinds of symbols.
But you can say all this time he was also having trouble because those symbols were not created by only one spiritual energy. The person who created those symbols uses two types of spiritual energy while creating them and because of this all this time even though Philip uses his technique in full power and also concentrates on that symbol, he is still unable to understand 100% about that symbol.