What is the purpose of offering a mass for someone? I recently made a donation to a Catholic organization and was told that, as a thank you, a mass would be offered for me. What does this mean? Does this mean that I have "sponsored" the mass in the same way that an organization might sponsor a television program? Is it a special kind of prayer for me? What is the purpose of offering a mass for someone?
What is the purpose of offering a mass for someone?

What is a Mass Intention?


  Mass Intention
  
  Definition
  
  The object for which a priest offers the Eucharistic Sacrifice. This intention is distinct from the priest's decision to offer Mass, which is necessary for valid celebration. It is also distinct from the effects of the Mass which benefit those who take part in the sacrifice and attend the Mass. These are called the special fruits of the Mass and extensively are without limit, as are also the effects on the entire Church, called the general fruits of the Mass. 
  
  Mass intentions refer to the particular purpose for which a specific Mass is offered. This may be to honor God or thank him for blessings received. But technically a Mass intention means that the sacrifice is offered for some person(s) living or dead. Also called the application of a Mass, it pertains to the ministerial fruits of the Mass. These fruits are both extensively and intensively finite in virtue of the positive will of Christ. Other things being equal, the more often the sacrifice is offered the more benefit is conferred. 
  
  The intention for which a priest offers a Mass is determined either by the common law of the Church, or by specific precept, or, most often, by the intention of the donor of a Mass stipend, or by the priest's own devotion. Since it is not absolutely certain that the ministerial fruits of the Mass are limited, a priest may conditionally (if the one giving the stipend suffers no loss thereby) offer the Mass for several intentions. It is assumed that the priest does not intend by these second or third intentions to fulfill an obligation of justice by these conditional applications. - Catholic Dictionary


At a concelebrated Mass each priest say Mass for a different intention.


  When a Mass is concelebrated, each priest offers the sacrifice of the Mass. This means that each priest is able to have his own intention. The fact that they are concelebrating i.e., offering their Masses at the same time and in the same location, does not alter the fact that each priest is celebrating Mass. - Canon Law Made Easy


In the end, the organization will have a Mass offered up for your intentions. My guess is that your name will be added to a list of benefactors of this charitable organization and that a special mass will be offered for all your intentions together, perhaps at a special altar or a particular time (Christmas).  

This tradition is also seen in St. Augustine’s Confessions (c. 397), where St. Monica (his mother) asks St. Augustine: “One thing only I ask you, that you remember me at the altar of the Lord.”


  Pope Paul VI said, “The Mass is the most perfect form of prayer!” It has immense power and countless miracles and conversions have occurred throughout the centuries by offering Masses for a specific intention or person. Mass intentions are a great treasure of the Church and have a spiritual weight that is incalculable. - What are Mass intentions?