To understand the weight of Episode 140, one must understand the context in which it takes place. By this point in the series (specifically Episodes 138 and 139), the narrative had shifted from the joyous victory of the Manalo Conference to a crisis of apocalyptic proportions. The Ultra Beast Guzzlord had appeared, threatening to devour the entire Alola region.
To the heroes' surprise, two "shiny" (white) Guzzlord also appear, increasing the scale of the threat. Pokemon Sun Moon Episode 140