The Catholic Church has always considered holy matrimony as a sacrament, and a sacrament it is. From marriage on, for the rest of our lives, sexual intercourse affirms this sacrament by  commemorating our marriage covenant – our vows of unity - that we had proclaimed that first night. After exchanging the marriage vows the husband and wife consummate those vows through sexual intercourse. This is their outward expression of an inward reality that spiritually combines their two bodies into one body that is sanctified to itself just as much as each of them were sanctified to themselves before marriage.    Married couples are set apart from anyone else and reserved in purity to celebrate the union of their body.

   This sanctity flourishes in an atmosphere where couples approach sex for the first time as comforting and celebrating one body (his and hers) without entertaining any kind of expectations of fantasies, but with erotically passionate love.  Once the proper reverence is shown, of course, couples can still have erotic fun in their sexual intimacies, but that fun should not be the focus to the point of obliterating the meaning of sex.  But couples without this understanding don't reverence sexual intercourse as a sacrament between themselves; they indulge in it purely for its recreational aspects and not with the proper reverence toward using sex as a commemoration of wedding vows.

  As I said, sex spiritually combines a married couples two bodies into one body that is sanctified to itself just as much as each of them were sanctified to themselves before marriage.  What I mean by this is that you view the purity of your body as something you can trust. Everyone - without exception - has a greater respect for the purity of their body than they do for someone else’s body.