A friend comes to you and says she has stopped going to Mass at her parish because she doesn’t get anything out of it.”
Mass is, first and foremost, about rendering due worship to God out of love for Him. If she isn’t “getting anything” out of Mass, it is likely (as you said) that she isn’t putting much
into Mass. This could be for any number of reasons. I think the first approach really has to be explaining the Mass to her in ways she might never have heard it explained.
The Mass is a participation in the heavenly liturgy. When we sing “Glory to God…”, we are echoing the words of the angels at the birth of Christ. When we sing “Holy, Holy, Holy”, we are singing the words which the angels sing eternally in Heaven before the throne of God.
The Mass is the “corporate” worship of God by the Church. By “corporate”, I mean “bodily”. (Latin
corpus = body.) The Mass is how the Church, as the
Body of Christ, comes together under her Head, Who is Christ, to worship the Father in the Holy Spirit. Every member of the Body is important, and no member of the Body can truly live apart from the Body. Although every member can do things on its own, it belongs with the rest of the members. (This is one reason why we are obliged to attend Mass.)
The Mass is the wedding celebration of Christ and His Bride, the Church. This wedding is portrayed for us in the book of Revelation: “Blessed are those who are invited to the marriage supper of the Lamb.” (Rev 19:9) Those words – well, words very close to them! – are said at Mass right before we receive Holy Communion. The Mass is an act of love: the Divine Husband offers Himself completely for His Bride, and she in turn offers herself to Him. (cf. Eph 5:25-27)
If she’s not “getting anything” out of Mass, perhaps she thinks of the Mass as simply a vehicle for giving her something, where she is
merely receptive. But the Mass truly requires something of
us.