Q. 1. I heard that there are occasions when a marriage in the Catholic Church may not be a Sacrament. How can that be possible?
A. 1. While such an occasion is rare, it does happen that a Catholic in good standing may marry in the Catholic Church, in a Catholic ceremony, and in accordance with Canon Laws, yet he/she does not receive the Catholic Sacrament of matrimony.
The Code of Canon Law # 1086 §1. states, "A marriage between two persons, one of whom has been baptized in the Catholic Church or received into it and has not defected from it by a formal act and the other of whom is not baptized, is invalid."
In other words, a marriage between a Catholic and a non-baptised person (this is not a Christian) is not valid. It cannot become a Sacramental Marriage.
Such a marriage can only take place in the Church with the permission of the Bishop who would be required to grant a dispensation from the Canon-law previously mentioned.
In the future, should the non-baptised person decide to convert to the Catholic faith, then in such an instance the marriage becomes sacramental once the baptism takes place. When such occurs, there is no need to implement a new Catholic ceremony.