12:2 Rashi- 

אשה כי תזריע IF A WOMAN HAVE CONCEIVED SEED — R. Simlai said: Even as the formation of man took place after that of every cattle, beast and fowl when the world was created, so, too, the law regarding him is set forth after the law regarding cattle, beast and fowl (contained in the previous chapter) (Leviticus Rabbah 14:1).

The purpose of this world is to bring ultimate repair to all parts of reality. Hence the Torah recounts the creation of these different parts of the world in ascending order of complexity, and in Vayikra it discusses the lower creations' rectification, through the process of eating. In Tazria, we learn of the next level of its repair, that of mankind, seeking the physical blemishes which indicate spiritual ones and tending to them.

13:14

וביום — Why is this word used (it might have said ובהראות)? To inform us that there are days when you may see (examine) the plague and there are days when you may not examine. On this account they (the Rabbis) said: A bridegroom is given a respite of all the seven days of the marriage festivities — to him, and to his clothing and his house (i.e. whether he himself or his clothing, cf. v. 17, or his house, cf. Leviticus 14:33 ff., has been affected by a leprous disease), and similarly on a festival he (everyone) is given a respite all the days of that festival — and during these periods the priest may not come to examine him or his clothing or his house (Mishnah Negaim 3:2; Moed Katan 7b; Sifra, Tazria Parashat Nega'im, Chapter 5 2; cf. Bekhorot 43b).

What a powerful concept is expressed here! Tuma and Tahara are put on hold for a Yom-Tov. Both on the national level and on the personal level, joy pushes away Tuma. Tuma indicates a distance from Hashem, and aYom Tov, is called a Moed, a time of meeting with Hashem.  Similarly, we learn an important lesson about the nature of a Chosson's rejoicing, that the Divine presence rests on a couple at the time of their union.  

13:46

בדד ישב. שֶׁלֹּא יִהְיוּ טְמֵאִים יוֹשְׁבִין עִמּוֹ; וְאָמְרוּ רַבּוֹתֵינוּ מַה נִּשְׁתַּנָּה מִשְּׁאָר טְמֵאִים לֵישֵׁב בָּדָד? הוֹאִיל וְהוּא הִבְדִּיל בְּלָשׁוֹן הָרָע בֵּין אִישׁ לְאִשְׁתּוֹ וּבֵין אִישׁ לְרֵעֵהוּ, אַף הוּא יִבָּדֵל (ערכין ט"ז):

בדד ישב HE SHALL ABIDE SOLITARY — This means that people who are unclean from other causes than that of leprosy shall not abide with him (Pesachim 67a; cf. Sifra). Our Rabbis said: Why is he (the leper) treated differently from other unclean persons that he should abide solitary? They replied: Because he, by slanderous statements, (cf. Numbers 12:10) parted man and wife, or a man from his friend, he must be parted from everybody (Arakhin 16b).

A person who speaks speaks devisively often feels hurt and alienated, and hurt by those he speaks about, even the ones whom he says, "It's ok, they're my friends." He doesn't realize that he is only causing more hurt and alienation in his wake. The perscribed cure for these Negaim to materialize what he's been causing and feeling all along, in the hopes that it will wake him to the immensity that he has caused, and to take steps to heal himself and the world at large. 

14:4

ד

טהרות. פְּרָט לְעוֹף טָמֵא, לְפִי שֶׁהַנְּגָעִים בָּאִין עַל לָשׁוֹן הָרַע שֶׁהוּא מַעֲשֵׂה פִטְפּוּטֵי דְבָרִים, לְפִיכָךְ הֻזְקְקוּ לְטָהֳרָתוֹ צִפֳּרִים שֶׁמְּפַטְפְּטִין תָּמִיד בְּצִפְצוּף קוֹל (ערכין ט"ז):

הרות‎ט CLEAN — This term excludes an unclean bird (of a species that may not be eaten) (cf. Chullin 140a). Because the plagues of leprosy come as a punishment for slander, which is done by chattering, therefore birds are compulsory for his (the leper’s) purification, because these chatter, as it were, continuously with a twittering sound (Arakhin 16b).

ועץ ארז. לְפִי שֶׁהַנְּגָעִים בָּאִין עַל גַּסּוּת הָרוּחַ (שם):

ועץ ארז AND CEDAR WOOD — This lofty tree was used because plagues come also as a punishment for haughtiness (cf. Arakhin 16a).

We've generally heard about slander/lashon hara as the cause, but there are a host of other causes as well. (Arachin 16a)  The Negaim appear to alert to the person that something is going wrong. You're damaging yourself, and your surroundings. You might be deluding yourself as to the seriousness of the situation. The point of the Negaim is to teach us that something must change. 

ושני תולעת ואזב. מַה תַּקָּנָתוֹ וְיִתְרַפֵּא? יַשְׁפִּיל עַצְמוֹ מִגַּאֲוָתוֹ כְּתוֹלַעַת וּכְאֵזוֹב

שני תולעת ואזוב AND CRIMSON AND HYSSOP — What is the remedy he should use, that he may be healed? Let him, abandoning pride, regard himself lowly as a worm (תולעת) and as hyssop (cf. Midrash Tanchuma, Metzora 3).

14:34

ונתתי נגע צרעת. בְּשׂוֹרָה הִיא לָהֶם שֶׁהַנְּגָעִים בָּאִים עֲלֵיהֶם; לְפִי שֶׁהִטְמִינוּ אֱמוֹרִיִּים מַטְמוֹנִיּוֹת שֶׁל זָהָב בְּקִירוֹת בָּתֵּיהֶם כָּל אַרְבָּעִים שָׁנָה שֶׁהָיוּ יִשְֹרָאֵל בַּמִּדְבָּר, וְעַל יְדֵי הַנֶּגַע נוֹתֵץ הַבַּיִת וּמוֹצְאָן (ויקרא רבה י"ז):

ונתתי נגע צרעת [WHEN YOU COME TO THE LAND …]I WILL PUT THE PLAGUE OF THE LEPROSY — This was an announcement to them that these plagues would come upon them (Sifra, Metzora, Section 5 4; Horayot 10a), because the Amorites concealed treasures of gold in the walls of their houses during the whole 40 years the Israelites were in the wilderness in order that these might not possess them when they conquered the land of Israel, and in consequence of the plague they would pull down the house and discover them (Leviticus Rabbah 17:6).

It's not just that there are riches in the walls. It's not just that there are silver linings to clouds, and everything is from Hashem. The person entering his house in Israel will still find Negaim, it's still going to be difficult, and most assuredly, it's going to happen. To me, tt's the promise that there will be dificult situations, and that's when we need to remember this the most.