Jesus’ teachings would have challenged even the most faithful Jews: suddenly it wasn’t enough to just meet the outward demands, it was now attitudes and thoughts that also mattered:
Matthew: 5:21-22 You have heard that our ancestors were told, ‘You must not murder. If you commit murder, you are subject to judgment.’ But I say, if you are even angry with someone, you are subject to judgment! If you call someone an idiot, you are in danger of being brought before the court. And if you curse someone, you are in danger of the fires of hell.