"If you do not redeem it, its neck should be broken." (Shemos 34:20)
If a firstborn donkey was not redeemed, its neck must be broken in the
back with a hatchet, and it has to be buried. No benefit can be derived
from it. From the way the Torah describes this procedure (Shemos 13:13-
15), we learn that it is parallel to Pharaoh's obstinacy in his refusal to
send us out of Egypt, which is referred to as "stiffness of the neck"
We learn from this that avoiding or neglecting a mitzvah does not lead to
any gain. In addition, we have a model of how Hashem sends retribution
upon those who stiffen their necks and remain stubborn against the
teachings of the Torah.