Rashi explains that these plagues are the result of evil talk, specifically the act of babbling words. Consequently, birds, which babble continually with chirping sounds, were required for true purification. The leper’s thoughtless chatter resulted in this plague. We may wonder at the necessity of using two birds. This message could be derived from one bird, as well. It seems similarly peculiar that only one bird was slaughtered, while the other was set free.
Apirion on the Torah explains that in order to answer these questions, we must first reflect upon the reasons for offering these sacrifices. The commentaries state that one who offers a sacrifice should consider the fact that the various sacrificial procedures performed with this animal (such as slaughtering, burning, etc.) should really have happened to the individual. In effect this animal takes the sinner’s place as a result of Hashem’s pity and beneficence. Thus, if one were to offer only one bird, which was to be later slaughtered, he would mistakenly think all forms of speech are evil. He would then “seal” his mouth forever as penance for his sins. This ludicrous form of contrition reflects a completely misguided perception of the responsibilities that accompany the power of speech. Man is not only permitted to speak words of Torah and other forms of “legitimate” speech, he is required to do so. Speech is a necessary component of expression. Appropriate self-expression serves an important role. Communication becomes repulsive only when it is used to slander others. This is the Torah’s message: one bird should die as penance for the individual’s evil speech, while the other should be set free. This symbolizes the sinner’s moral obligation to use his power of speech for constructive purposes.
