“two live birds, of the pure species.” (VaYikra 14,4)
All “pure” birds are known as צפור. We know this from Devarim 14,11: כל צפור טהורה תאכלו, “you may eat all the birds belonging to the species known as צפור טהורה.” This excludes birds known as עופות טמאות. This means that although the bird itself has all the symptoms of purity, the fact that it has been associated with forbidden practices such as birds belonging to people of an עיר הנדחת, “ a city condemned to destruction because the majority of its inhabitants worshipped idols,” makes such a bird “unclean.” Or, for instance, if such a bird of the “pure species” killed a human being, it also forfeits its status of being a צפור טהורה and may not be eaten or used as an offering.
A Midrashic approach (compare Tanchuma Metzora 3) to the wording in our verse: G’d said that the sacrifice to be brought by people who have overcome their affliction should consist of birds which twitter a lot so as to remind the person offering this sacrifice that the indiscriminate use of their tongue had been the cause of their suffering the affliction in the first place. In other words: “let the sound of the bird atone for the sound made by its owner.”
“and here the affliction is on the walls of the house.” (Vayikra 14:37)
Up until this point the Torah had listed 10 different kinds of negaim, afflictions; six of them occur on the body of a person; they are שאת, ספחת, בהרת, שחין, נתק, מריטת הראש. Four additional afflictions infect things other than his body such as woolen garments, linen garments, leather garments or utensils, and the walls of a house.
You will find that the ten are arranged in the order in which we just mentioned them. There is a correlation here to the Ten Commandments. The message is that as long as the Israelites observe the Ten Commandments, i.e. the Torah which the Ten Commandments represent, they will not experience any of these ten afflictions. If they fail to honor the Torah and it’s precepts they will become victims of what the Torah has listed in the way of nega-im.
“This is the legislation for every tzoraat affliction and the netek; and afflictions on the garments and the house; and of the se-eth, the sapachat, and the baheret.” (VaYikra 14,54)
Even though the tradition handed down to us concerning all these laws is the reliable one, i.e. that the sequence in which G’d afflicts potential victims is that first He afflicts their houses to give them a chance to repent, followed by afflictions on the garments hoping that the sinners will mend their ways, and that only as a last resort does G’d afflict the bodies of the sinners concerned, the fact remains that in the written Torah the order is reversed, the Torah commencing the legislation with skin disorders, followed by similar disorders on the garments followed by the houses which display signs that the walls are afflicted.
The reason the Torah chose to write the sequence which we find before us rather than the sequence our sages have told us, is that the Torah’s ways are ways of pleasantness (Proverbs 3,17). Had the Torah followed the reverse pattern of reporting these kinds of afflictions we would have read of matters going from bad to worse; this would not have made for edifying reading. As it is, the Torah first lists the most severe afflictions, proceeding to describe afflictions which are progressively easier on the victim, i.e. that only his garments or the walls of his house undergoes an affliction.