If the person is already Christian, then they are familiar with the bible. IMO, if you explain briefly the format of the Mass from a Protestant perspective … the bible … they would appreciate the Mass.
For instance, the Mass is straight from the bible. And it consists of two parts.
The first part are Bible readings. There are three readings taken from the OT, from the letters, and from the Gospels. These Bible readings are the same throughout all the Catholic Masses world wide. Between readings are hymns, psalms, and other short responses. After the third reading, a spiritual explanation of the readings is given.
After that, the second part begins the Last Supper. Bread and wine are brought to the altar, the priest offers a prayer of blessing over them, and then says the words of Jesus at the Last Supper changing them into the Body and blood of Jesus. The priest has this power thru the laying on of hands from those who had previously been given this power, reaching back to the time of the apostles. After that, the people receive the Body and Blood of Jesus just as the apostles did at the last supper. Jesus said, “he who eats my flesh and drinks my blood lives in me and I live in him.” Then the Service is concluded with a meditative thought and a hymn.
In summary it is receiving the Word of God spoken, and receiving the Word of God himself.