But: this indicates contrast with the case where the mildew has spread (verses 44-47).

If the priest comes …: the conditional if does not refer to the coming of the priest but to the absence of mildew in the newly plastered house. The idea is “When the priest goes to examine the house, if the mildew has not spread, then….”

Quoted with permission from Péter-Contesse, René and Ellington, John. A Handbook on Leviticus. (UBS Helps for Translators). New York: UBS, 1990. For this and other handbooks for translators see here .