If a woman has conceived and born

This section of the Torah, which deals with the laws of childbirth, comes directly after that portion which spoke of unclean animals--those which died of themselves, creeping things and insects. We learn from this that in the same way that eating non-kosher food makes a Jew dulled and insensitive to holiness, the opposite is true. Keeping the laws of kashrut ensures that one’s children will be spiritually healthy and sound. (Ramban)