Leviticus 14:4

חיות LIVING [BIRDS] — This term excludes רפות‎ט, birds that suffer from some fatal organic disease (חיות does not only mean “living”, but also “capable of continuing to live”). 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 AND CEDAR WOOD — This lofty tree was used because plagues come also as a punishment for haughtiness (cf. Arakhin 16a). ושני 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). עץ ארז means a stick of cedar wood (not a cedar tree). שני תולעת — a strip of wool dyed crimson.

then shall the priest command to take for him that is to be cleansed two birds alive and clean, and cedar wood, and scarlet, and hyssop:

וְצִוָּה֙ הַכֹּהֵ֔ן וְלָקַ֧ח לַמִּטַּהֵ֛ר שְׁתֵּֽי־צִפֳּרִ֥ים חַיּ֖וֹת טְהֹר֑וֹת וְעֵ֣ץ אֶ֔רֶז וּשְׁנִ֥י תוֹלַ֖עַת וְאֵזֹֽב׃