Metzora

The פסוק says ונתתי נגע צרעת בבית ארץ אחוזתכם.
The Sifsay Chachamim asks, why does it say ונתתי נגע, & I will place a נגע, inferring that it’s a good thing. It should have said, when there will be a נגע. Rashi explains that it really is a good thing, for the אמוריים hid all kinds of treasures in their houses while the jews were in the desert, and when they get a נגע they’ll have to break down the house & will find the hidden treasures. So in reality its good. The כלי יקר quotes the gemara in ערכין that says, afflictions of the home come because of צרות עין – stinginess. Hashem gives a person a lot of good to see if he will share with others, showing that He believes it’s all His money that was given to us to distribute. That’s why the next posuk says ובא אשר לו הבית, If the house is only לו,to him, & not to share, then the נגע will come. ר'משה פיינשטיין asks, how is it possible to understand this? If house negaim come from being stingy, how could it be that he’s rewarded for sinning, with wealth-the very thing he sinned with?
The ערוך השלחן answers that this is how Hashem shows his love for us. Even when He has to bring yesurim, although he doesn’t want to, He does so only to make the person realize he’s doing something wrong & should change his ways. The troubles a person has are for his eventual good. Like by yosef when he was sold he thought the worst, still it turned out for the best.
Here too, even though seemingly a נגע בבית is a bad tiding, Rashi explains that even though tzara'as comes because of sin, eventually it will be good. For a person will find the treasure & say to himself, had I not sinned I would have gotten all this without the yisurim, & better himself for the future, teaching us that no matter how bleak things may look we have to realize it’s all for our good. Like the one who got tzara'as thought it's the worst thing, but then found gold. So too one day we'll see how all our problems were really just to get the gold!