Literally telling the reader how it was able to pierce right through.
"Hurled by the mightiest arms in Asgard, the gleaming blade hits its mammoth target, piercing the Celestial's chest with such force it passes completely through."
One would have to completely ignore this very explicit scene to come to another conclusion. When you marry this page with the next, common sense should tell you that Arishem did nothing in particular, did nothing extra, did nothing in specific to prevent the sword from piercing him. Why, because he most likely knew it would be inconsequential. The Celestials in this arc were treated beyond skyfathers. Taking just one piece and completely glossing over other relevant facts is nitpicking.
Y'd u guys close that thread? It was overall pretty civil by leaps and bounds compared to many others here.