Many complexities and difficulties accompany "mixed marriages", i.e. between a Catholic and a baptized non-Catholic. These difficulties, the Catechism says, "must not be underestimated. They arise from the fact that the separation of Christians has not yet been overcome. The spouses risk experiencing the tragedy of Christian disunity even in the heart of their own home" (1634). According to Church law, such marriages cannot be licitly contracted without the express permission of the proper authority (usually the local bishop), who is not to grant it unless the Catholic party is ready to protect his or her own faith and sincerely promises to do all in their power to have the children baptized and educated as Catholics (cf. cc. 1124-25).
The book of Genesis contains two accounts of the creation of the sexes and the institution of marriage. "God created man in his own image...; male and female he created them. And God blessed them, and God said to them, 'Be fruitful and multiply'" (Gn 1:27-28). "Then the Lord God said, 'It is not good that the man should be alone: I will make him a helper fit for him'... [and God made woman]. Then the man said, 'This at last is bone of my bones and flesh of my flesh'... Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh" (Gn 2:18-24).
Marriage was instituted by God from the start of creation (Gn 1:27-28, 2:18-24). It represents a major part of the divine design for the good of persons - of the spouses and children - as well as of society.
For Christians marriage is much more. It is also a sacrament, one of those "efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us, [and which] bear fruit in those who receive them with the required dispositions" (CCC 1231). Marriage between Christians is therefore a source of grace. "Since it signifies and communicates grace, marriage between baptized persons is a true sacrament of the New Covenant" (ib. 1617).
Life is about getting to know and love God. Our starting point to know him is creation, particularly the masterpiece of visible creation: the human race. Each individual human, male or female, is made in the likeness of God. Man and woman each "images" God, in a different though complementary way. Considered together in their complementarity, they give a fuller image.
Although there is no sexuality in God, his creation of man as a sexually diversified being, also gives a key to what God is. An understanding of what it means to be masculine or feminine is essential in order to learn from a major revelation of himself inscribed by God into creation.