What did Renfield do to lead Dracula to attack him?

The dying Renfield tells them that on the night the men went to investigate Carfax, Dracula appeared and offered him countless lives to feast on if Renfield would fall down and worship him. The madman gave the vampire the invitation he needed to enter the asylum; after that, the vampire did not give Renfield any of the promised lives. Two days later, Renfield saw Mina and realized that she had been drained. So tonight, when Dracula entered, Renfield tried to fight with him. The vampire's eyes burned him and deprived him of his strength, and Dracula flung him across the room.