Ow and why did marriage become a sacrament?

A clear line of argument needs to flow through the essay, with each paragraph moving the argument forward by one point. Points to be addressed within the essay:
-When exactly did marriage become a sacrament?
-What had its status been previously?
-What were the processes and formalities?
-Was there debate? If so, on what grounds and using what materials?
-Was the motive simply divine inspiration, or were more mundane ambitions at work?
Reading:
-J. Murray (ed.) Love, Marriage and Family in the middle ages
-J. Richards Sex, Dissidence and Damnation: Minority groups in the Middle Ages
-G. Duby Love and Marriage in the Middle Ages (ch. 3,4,6)
-J.A. Brundage Law, Sex and Christian Society in the Middle Ages (ch. 5-9, 12)
-D. dAvray Medieval Marriage: Symbolism and Society