The group told Gravis what they went through in their first trial. They had to defend themselves from an army of beasts that grew more and more numerous as time went by, without any pause. Gravis immediately saw the similarity between that trial and his mad dash for power back in his homeworld. Back then, he had willingly put himself in a similar situation.
That mad dash for power had helped him in condensing his initial Will-Aura. After all, it was good tempering, and it gave a lot of combat experience. The group had to adapt to waves of beasts that continually got stronger to survive.
This confirmed Gravis' thought that Heaven was putting the group through the perfect trials for them. After all, they had three people that went through the tenth level of Energy Gathering. They were probably more valuable to Heaven than all the other groups combined. In total, their trial had been going on for one month.