A marriage relationship consists of four basic aspects: communication, relational, physical, and spiritual.  If a couple goes to a marriage counselor, the counselor will usually try to help the couple with the first three aspects in their relationship, but rarely will they address the spiritual.  But marriage is first and foremost a spiritual union, so this is what needs to be addressed first.  The physical aspect of the marriage is the last aspect to address because, in most situations, it will reflect what is happening in the rest of the marriage. 

It has been said that the eyes are the window to the soul.  God, Who created human persons in love, has given married couples a way to unite in both body and soul in the conjugal act.  Of all the physical creatures God made, human persons are the only ones who look at one another in the act of procreation.  So, the couple can literally see the love of the other person in and through the eyes while at the same time they can feel that love in their bodies.