"ומקלל אביו ואמו מות יומת"
"One who curses his father and mother will be executed."
In the olden days, the power to decide life and death was in the hands of the father. The Torah gave it over to the judges. But the Torah is stricter with children because they were accustomed to strict judgments. However Torah Shebial Peh makes it especially difficult to carry out the death penalty by making many conditions which are almost impossible to fulfill. For example, one is only liable for cursing one's parents if he uses Hashem's explicit name [שם המפורש].
The parsha goes from the most severe to the least severe. Killing any person, striking a parent, stealng a person and selling him, cursing a parents [which is mere speech].
ולענין סמיכת הפרשיות נ״ל שהכתוב הולך מן הקשה אל הקל, פתח ברוצח (מכה איש ומת) ופירש פרטיו (שוגג ומזיד), אח״כ הזכיר מכה אביו בלא מיתה, ואח״כ גונב איש שאינו ממיתו אך משעבדו כעבד, אח״כ הזכיר מקלל אביו, שהוא דבור בעלמא, ומ״מ הוא במיתה.
