Christ teaches us many things in the gospels, but perhaps none as clearly as his stance on divorce and remarriage. Simply put, remarriage after divorce is not allowed by Christ. See Mt 5:31-32, Mt 19: 1-12, Mk 10: 1-12, Lk 16:18, I Cor 7: 10-11. For more information see the Biblical Foundation page. The early Christian communities held fast to these words of Christ, and the Church fathers echoed them throughout the centuries. From the earliest times the Church had a policy of one attempted marriage and that’s it, no second chances.
The process for a declaration of nullity has its roots in the New Testament. See I Cor 6: 1-6. Bishops in the early Church judged marriage cases themselves. The process for a declaration of nullity, as it is known today, developed in the middle ages from a combined study of Roman law and ancient Church teaching. Through this more formal process Christians had the means available to them to make a legal argument that their marriage was invalid. Therefore, the process for a declaration of nullity should be seen as an advancement in Church discipline which has opened up the possibility of entering a true marriage after a failed and invalid one.
The constant and ancient teaching of Christ and His Church is that marriage is a permanent and exclusive relationship. However, we live in a culture which has denied these basic realities. The Church today finds herself in a position where she has to either uphold authentic Christian teaching or cave under the cultural pressure of allowing divorce. We can be assured that, through the grace of God, the Church will remain faithful, and continue to proclaim the permanence of marriage.