Lévitique 14:4

Then the priest shall direct that he who is to be cleansed take two birds, alive and clean, and wood of the cedar, and scarlet (wool), and hyssop.

he shall take, for the one purifying himself i.e., the kohen shall take it from the other’s property (although one could also say that the person formerly afflicted with ṣara‘at shall first give it to the kohen). In the word the one purifying himself the tav of the reflexive hitpa‘el is absorbed into the doubling of the following ṭet ; but the word is truly reflexive, as in “one who boasts” [Hebrew: mit hallel] [Proverbs 25:14].

two birds All species of fowl are denoted by the term birds , and he may take any available fowl, so long as they are:

alive i.e., not dead; and ...

ritually pure — he may not take from the ritually impure species [11:13-19].

a cedar stick…and some hyssop These are the largest and the smallest of the species of plants, and we know this from the verse describing Shlomo’s knowledge [I Kings 5:13]. (The word hyssop is known to us through tradition, and we do not need to investigate its meaning.) Thus the sufferer of ṣara‘at , and the infected house [:49], and the ritual impurity of a corpse [Numbers 19:18], all resemble one another; and they all relate distantly to the Paschal sacrifice observed in Egypt [Exodus 12:22].

THEN SHALL THE PRIEST COMMAND TO TAKE FOR HIM THAT IS TO BE CLEANSED TWO LIVING, CLEAN ‘TZIPORIM’ (BIRDS). “Living, this excludes birds which are treifah. according to the accepted opinion (see Note 9 below), is an animal or bird suffering from one of certain organic diseases from which it is bound to die within twelve months, even though it be ritually slaughtered. Thus the word living excludes a bird which will die from a disease. Ramban further on will comment on this point. Clean, this excludes a bird unfit for food. Since the plagues of leprosy came as a punishment for slander, which is done by chattering, therefore Scripture required for the leper’s cleansing that he bring birds which always twitter with a chirping sound.” This is Rashi’s language.
Now in view of the fact that Rashi wrote, “Clean, this excludes a bird which is unfit for food,” we can deduce that the [unqualified] term tziporim does not denote a permissible species of birds, but is instead a generic term for all birds [those permissible as food and those forbidden]. If so, the question appears: what is this “chirping” that they found [among the tziporim]? For there are many birds among which there is none that openeth the mouth, or chirpeth! Moreover, the interpretation [which Rashi quoted]: “Living, this excludes birds which are treifah,” according to the accepted opinion (see Note 9 below), is an animal or bird suffering from one of certain organic diseases from which it is bound to die within twelve months, even though it be ritually slaughtered. Thus the word living excludes a bird which will die from a disease. Ramban further on will comment on this point. is really subject to a controversy of opinion, animal or bird can in fact survive for more than one year. and according to the Sage who says that a treifah according to the accepted opinion (see Note 9 below), is an animal or bird suffering from one of certain organic diseases from which it is bound to die within twelve months, even though it be ritually slaughtered. Thus the word living excludes a bird which will die from a disease. Ramban further on will comment on this point. can survive, this interpretation [of Rashi] is not correct. And in the Torath Kohanim we find this interpretation: 1:12. “Living, not slaughtered. Clean, not unfit for food. Clean, not treifoth.” means not …

ולקח למטהר שני צפרים, “and he will take for the person to be ritually cleansed two birds;” according to the Talmud in Erchin folio 16, the offering matches the sin for which it is to atone, i.e. just as birds engage in constant useless chatter, so the tale-bearer to be cleansed now had done something which had demeaned his power of speech to something no better than that of a bird.