Each time I come back after being away it appears more like a sepulcher! The "whited" one of the Bible—pagan temple front stuck like a mask on Puritan gray ugliness! It was just like old Abe Mannon to build such a monstrosity—as a temple for his hatred.
Christine complains of the sepulchral nature of the Mannon house in Act I of "Homecoming." The house is of course the tragedy's primary mise-en-scène. It functions as crypt to the family's secrets. Christine refers to this secret history in cursing Abe Mannon, who built the house to cover over the disgrace that sets this revenge cycle in motion. Thus the temple to Abe's hatred is also a monument of repression.
As Christine laments, its distinguishing feature is its portico, what the stage notes describe as the "incongruous white mask" hiding its ugliness. This mask makes doubles out of its residents, evoking the "life-like masks" the Mannons wear as their faces. Thus Christine personifies the house when she describes it as a "whited sepulcher." Here Christine alludes to a simile Jesus uses in Matthew 23:27 in condemning hypocrites exemplified by the scribes and Pharisees. In common usage, the metaphor refers to an evil person who hypocritically pretends to be holy or good.