Whenever I read the first chapter of Genesis, in which the first creation account of man is given (a slightly different version is given in chapter two), I am reminded forcefully of God's trinitarian nature and the profound importance of that for how I view my marriage.
God created man in his image; in the divine image he created him; male and female he created them. (Genesis 1:27)
We know from some of the early Church councils that God is a trinity: three divine persons, Father, Son, and Holy Spirit, with one nature. The very nature of God allows for only one God. Thus, the three persons are one god, not three gods.
This account of God's creation of man, male and female, in his image reveals the familial nature of God's own being. God is a communion of persons, with the Father and the Son, with the Holy Spirit proceeding forth as the love between them. That is the image in which man is created, male and female. Man is not meant to be alone. The male and the female complement one another in completing the image of God.
And that's where I find that the trinitarian nature is important to how I see my marriage. My marriage is a living icon of God, with the husband and the wife and the love between them proceeding forth as the fruit of the marriage (children). Divorce is painful to witness because it smashes this trinitarian icon (although it could be argued that the smashing occurs earlier, when the love between the spouses dissolves).
Some people live their lives assuming that the dogma of the trinitarian nature of God has no real bearing. For me, it means everything! It is one of the central tenets of our faith, and runs through everything that we believe as Catholics.
And it starts with the very first chapter of scripture.