Did you know...

When a priest offers Holy Mass, he has three intentions: First, to offer the Mass reverently and validly in accord with the norms of the Church. Second, to offer the Mass in union with the whole Church and for the good of the whole Church. Third, to offer the Mass for a particular intention. Most commonly the intention is for repose of the soul of someone who has died. However masses may also be offered for the living as in prayers for healing, or birthday or anniversary blessings.

The tradition of making an offering in exchange for the priest's intentions goes back to the early days of the church. This stipend, given to the priest for offering the Mass, thereby in justice creates an obligation which must be satisfied.

excerpted from https://catholicexchange.com/what-are-mass-intentions-2/