like peering into an abyss; as if standing on the edge of an abyss
A classical simile evoking the awe and danger of confronting a deep, unfathomable situation. Used in literary or formal contexts.
His eyes were like peering into an abyss; I couldn't read his thoughts at all.
深淵 is the noun 'abyss'; the full expression is a fixed simile.
如し is the classical auxiliary meaning 'like/as if'; the expression uses its classical form.
From the Classical Chinese phrase 如臨深淵, “as though approaching a deep abyss,” found in the Book of Odes and quoted in the Analects as an image of extreme caution.