A few days Innocent Duru, on an old post concerning Parochial Vicars, asked a question about the Holy Mass offered pro popolo, that is, for the people.
This obligation is given in the Code of Canon Law:
After a pastor has taken possession of his parish, he is obliged to apply a Mass for the people entrusted to him on each Sunday and holy day of obligation in his diocese [not every diocese observes the same days as obligatory]. If he is legitimately impeded from this celebration, however, he is to apply he is to apply it on the same days through another or on other days himself (canon 534 § 1).
Regrettably, this obligation seems to be observed more in the breach than in the norm, at least in places with which I am familiar. This is likely due, in no small part, to the practice of grouping several Mass intentions together at one Mass.
It has long been customary for the faithful to ask priests to offer the Holy Mass for particular intentions and to offer a small gift to the priest to help with his sustenance. The custom of Mass intentions is governed by the Code of Canon Law:
In accord with the approved practice of the Church, any priest celebrating or concelebrating is permitted to receive an offering to apply the Mass for a specific intention..
It is recommended earnestly to priests that they celebrate Mass for the intention of the Christian faithful, especially the needy, even if they have not received an offering.
The Christian faithful who give an offering to apply the Mass for their intention contribute to the good of the Church and by that offering share its concern to support its ministers and works.
Separate Masses are to be applied for the intentions of those for whom a single offering, although small, has been given and accepted.
A person obliged to celebrate and apply Mass for the intention of those who gave an offering is bound by the obligation even if the offerings received have been lost through no fault of his own (canons 945-949).
To assist the faithful in decided what offering should be made, the Province of Bishops is able to set the usual amount of the offering. The Bishops of the Province of Illinois set the offering at $10.00 per Mass. A person is able to offer the priest more or less to accompany a Mass intention, but a priest in this Province cannot request more than this amount and he should certainly not refuse a smaller amount.
The pastor of a parish is required to offer the Mass pro popolo, for his parishioners, because it is right and just for a father to pray for his family.
Father William Saunders has written an excellent article explaining the theology behind the offering of Mass intentions and stipends.