What else should he do with the live bird? It makes sense that if one bird dies and the other bird lives, the live bird be turned loose to live out its life. Simply, the reason the Torah underscores the freedom of the live bird is that originally it had been designated as a sacrifice. In the end, it worked out that it was not used for this purpose. I might think that once the term korban, sacrifice, has been designated on a bird, it has been spiritually elevated, thus prohibited for mundane use. The Torah is teaching us that, regardless of its original designation, the bird should be set free. It will never be used, allowing for its designation to dissipate.
Horav Moshe Aharon Stern, zl, gives an inspirational explanation of why the Torah emphasizes the bird’s freedom. It was “washed” in the blood of its co-bird. When one washes himself in his friend’s “blood,” a special pasuk is required to permit the bird for ritual use. What a powerful insight – and how (sadly) practical. Can we declare with clear conscience that our ascendency, success, good fortune did not come as a result of a friend, another person who did not make it? While this is not a reference to intentional harm, we cannot deny that, at times, the choice boils down to two people: one makes it; the other “also ran.” We Jews believe that it is not due simply to the “toss of the dice;” rather, someone’s shoulders became our stepstool. That should at least engender a sense of introspection and humility.