Jesus claims in Matthew 19:3-12 the only case in which people may divorce is porneia. The New American Bible translates this word very generally as unlawful. It seems that any infraction of Church canons regarding the legitimacy of a marriage would give grounds for divorce. Biblical scholars, however, find a much more restrictive meaning: an incestuous relationship. St. Paul attests to this among Christians in Corinth and insists not that the people may divorce but that they must.
The Church rightfully upholds the indissolubility of marriage. It is plain that God wills marriage to be exclusive and for life. At question is if the Church is correct in making as many exceptions as she does. Many ridicule the Catholic Church for doing so and call annulment a “Catholic divorce.” However, the Church has an exulted view of marriage that goes beyond superficial promises and physical consummation. She expects people to know what they are promising, to believe in what they say, and rely on the help of the Holy Spirit to fulfill their duties. Anything less is not a true sacramental marriage.
Because marriage is central to human life, it must be safeguarded with extreme care. The Church does so by providing marriage preparation. An annulment is allowed after investigating whether a valid consent to marry has been made. Sometimes a couple intends only a part of what sacramental marriage is by holding out the option for divorce, if they no feel in affection based love. Others are unable to fulfill their vows due to character disorders, alcohol/drug addiction or mental illness.
Divorce is not in the best interest of the child, except in danger of abuse or the above mentioned human faults. The Church so carefully guards the sanctity of marriage that she begins by assuming the marriage was valid, and then investigates the validity of the marriage. In annulment the Church determines that a sacramental marriage never existed.