Jewish marriage has two steps (the second step, "nesuin," will be studied later in the book). The first step is called "KiDuSHin," which comes from the same root word as, "KoDeSH (holy, sanctified" - right away we see that marriage is axiomatically and intrinsically a holy state) and "heKDeSH (designated for a holy purpose, and separated from any other purpose)."
Before we get to any discussion of holiness in marriage, let me point out that there is a mitzva in the Torah (Leviticus 19:2) "Be holy as I G-d am holy." Ramban (Rabbi Moshe ben Nachman, 13th century), in his classic commentary on the Torah, wrote that you may be able to keep every technical mitzva in the Torah and miss the point. His famous example is of the person who only eats flawlessly kosher food, but he shovels it in like an animal. The Torah says that this "kosher" fellow is a "low-life within the domain of the Torah," which is not the goal of the Torah. Since this is not good enough, G-d included in His Torah the commandment to be holy. To "get by on technicalities" does not work. We have to fill in all the blanks or the gaps. How? With holiness.
Rabbi Shimshon Rafael Hirsch (1808-1888) was one of the greatest articulators of Torah. His knowledge of Hebrew grammar was brilliant to the point of uncanny. His knowledge spanned Bible, Talmud, midrashim, ethics and law. In his brilliant commentary on the Torah, he elaborates on the commandment to be holy. To be holy means to separate from, and rise above, this world. The Torah doesn't command us to stop being human or to eradicate human nature. The goal of the Torah is to bring us to fully control our human personality and to use it for the good and for the spiritual. The Torah commands us to channel, elevate, moderate and direct the forces and powers in the human personality. Holiness means rising above the nature of this world.
Let's go a step further. Why? And, what is our model? G-d Himself. We must emulate His spiritual essence and characteristics, not only in what we do, but in how we do it. Holiness elevates both action and state of being. G-d's holiness itself provides the imperative for the Jew to be holy in all things.
Getting back to marriage, we have "double duty," in the holiness domain: 1) the basic and universal imperative to behave and grow spiritually and with holiness at all times, and 2) the specific imperative to fully conduct marriage as an undertaking in holiness, as defined by G-d's Torah.
Marriage, by definition, requires that each partner elevate above the habits, temptations, assumptions and pulls of this world; perhaps more than in any other aspect of life. The conduct of the marriage, the treatment of the partners, and the atmosphere in the Jewish home are to be holy. Each Jewish spouse should be able to discern that G-d is behind the way spouses basically treat each other and the way the marriage and home basically operate. The marriage can allow an occasional forgivable human foible or booboo arising out of the imperfections of its human inhabitants.
When one would make property "hekdesh," he would sanctify it for use in the Holy Temple. In Torah law, once you designate a contribution (e.g. an animal for a sacrifice) as being "hekdesh," it may no longer be used for any private or secular purpose.
This gives an insight into the holiness particular to marriage. The spouse is exclusive to the partner and to the marriage. Like hekdesh, marriage is not there for selfish, personal purpose. The partners are designated to each other and their holy union, to the exclusion of the entire rest of the world.
Hitler had indoctrinated the Germans with the idea that they were the "master race." During the war, the Klausenberger Rebbe was a concentration camp prisoner. He encouraged a Jew who was crumbling under the Nazi torture by telling him to never forget that he is from the "Chosen People." A German guard overheard the Rebbe and, since Yiddish is similar to German, he understood what the Rebbe said and became infuriated. "So, you think you are the 'chosen people'?" The Nazi brutally beat the Rebbi with his rifle butt till he fell to the ground. The Nazi then roared, "Do you still think you are the 'chosen people'?" The Rebbi said, "Yes, more than ever, because I could never do to another human being what you just did to me!"
The Torah commands us to be holy (Leviticus 19:2). Becoming holy requires overcoming the sinful forces inside us, which stem from the physical world, that pull at us [Rashi]. A major part of being a Torah Jew is to want to be incapable of causing hurt or harm to another. This comes from working on midos.
Constantly working on midos is vital in all interpersonal relationships, in general; and how much moreso in marriage, in particular! Menoras HeMeor writes that the midos of the parents influence and mold the children. It is vital to constantly and vigilantly demonstrate fine midos at all times - for the wellbeing and wholesomeness of yourselves, your marriage and for your children. This applies for doing good AND for refraining from bad; to treatment, speech, tone, and the feelings that are conveyed and caused. Midos are instilled in those who see you and in the next generation, so midos have far-reaching ramifications. You are a link in a chain of Jewish generations, tradition and spiritual continuity. You should strive to mold the next generation into being what the previous Torah generations were. When spouses give over love; to spouse, to children, in his and her general mode of operating; this creates a love-atmosphere; and this love goes over to your children and on for generations. The tone that you set in your house is what your children learn and absorb - AND give over when THEY are spouses and parents.