Moses told the Jewish people, "When you build a new house, you must make a railing for your roof."
This law can be interpreted to apply to a newlywed couple about to embark on the exciting challenge of building a household. The Torah counsels the couple that they are commencing a new phase in their lives, with new responsibilities and tasks that they have never yet had to face. This new and intensified focus on life in the physical world is a "descent" relative to their previous, single lives, and they are therefore poised to fall from the previous spiritual level unless they take preventative measures.
Therefore, they must "make a railing," i.e., put in place new spiritual safeguards in their observance of the Torah's commandments, not relying on their previous ones alone. Maintaining and enhancing their study of the Torah and observance of its commandments will ensure that the euphoria of the wedding day continue throughout their married life.