John Gill Commentary Leviticus 14:39

"And the priest shall come again the seventh day, and shall look; and, behold, if the plague be spread in the walls of the house;" — Leviticus 14:39 (ASV)

And the priest shall come again the seventh day, and shall
look
On the seventh day from his shutting of it up, he shall open it again, go into it, and observe in what condition it is: and, behold, [if] the plague be spread in the walls of the house:
the hollow strakes are become deeper, or the coloured spots are become larger: spreading was always a sign of leprosy, both in the bodies of men, and in garments.