Lucifer hadn't yet explained that each Aspect embodied a particular feature of its concept, so while Arthur had sensed it instinctively, he hadn't realised that it was the defining feature of his Destruction Aspect he'd been perceiving.
After Barda's explanation, it all clicked immediately.
Arthur only needed seconds to realise Selective Destruction was the defining feature of his Destruction Aspect—its 'Aspectual Authority'.
This was what he'd used earlier to counter Baruuk's strange Aspectual Authority, which had been channelling Arthur's own energy to repeatedly damage him in the spots Baruuk had successfully struck, surprising Baruuk.
Normally, dispelling Baruuk's Aspect-powered destructive energy would involve some degree of self-harm, especially since it consumed the target's energy to function, but Arthur could simply exclude himself from the damage, allowing him to destroy the destructive energy without injuring his own body.
