In the RoS cinematic Malthael pays no mind to the sword and, as he is moving towards Tyrael, lets El'druin trespass him. However, no damage is dealt.
Could this mean that Malthael, despite being a villain, has a righteous intent? Does it mean El'druin cannot affect Angels (although it could harm Izual)? Or is it simply Blizzard ignoring the lore in order to show us how powerful/badass/awesome Malthael is?