The husband and wife relationship in the Torah is completely different to any other. Two strangers come together and through marriage, create the closest familial relationship to the point where they become one (Breishis 2:24.)
The Midrash (Breishis Rabah 1:14) says for 26 generations the aleph complained before Hashem’s throne saying: I am the first letter and You did not create Your world with me.
Hashem replied that the world and its’ contents were only created in the merit of Torah and it will open with you as it says: Anoichi Hashem (I am God.)
In other words Aleph would be given a much more important place as the first letter of the Aseres Hadibros (Ten Sayings – wrongly translated commandments.)
Why then does Torah start with the letter Beis?
Breishis (the first book of the Torah) is about the creation of the physical universe. The letter Beis (first letter of Breishis) has a gematria (numerical equivalent) of two (see Spiritual Unity in Judaism.)
The physical universe is composed of opposites – light/ dark, hot/ cold, night/ day. These opposites are the catalysts of all growth and life.
Growth or change in the physical world takes place through the binary battle of opposites, positive/ negative, male/ female, empty/ full etc.
The purpose of the world, on the other hand is beyond the physical in the spiritual. In particular, it is to reveal the spiritual in and through the physical.
Spiritual is by definition Unity. Hashem (God) is the Root Cause of all (One is H’ on the heaven and the earth because He alone is the Cause of everything.) Hashem is constant, no change, One.
The Aseres Hadibros are category headings of all the Mitzvos (commandments) (see Even Ezra; Shmos 20:1) and are thus vessels for spirituality in this world (see Ten Commandments of Judaism.)
The first dibra (saying) underlies all the others in that all the other mitzvos are meant to be done exclusively because Hashem said so (Even Ezra Op.Cit.)
As tools of spirituality and thus the purpose of the world they have a greater importance than the physical creation. The Aseres Hadibros start with Aleph (the first letter of Anoichi (I am.)
Therefore Torah begins with Beis as the building block of the physical world and ends with Yisrael (Israel – the Jewish people) the model (through keeping of Torah and mitzvos) of unity in a binary world.
Man and woman come together in marriage to form one soul (or in the ideal scenario re-form the one soul they originally were) – ie. two opposite physical bodies unite to form one spiritual entity.
This can only happen through the husband and wife relationship and is the consummate realisation of the purpose of the world and the paradigm of the beis of Breishis working to the purpose of the Aleph of Anoichi.