One chooses music for Mass according to liturgical, musical, and pastoral appropriateness. Liturgically, the music ought to fit the form of the liturgy. For example, what season or feast is it? What is the gospel of the day? What is the liturgical moment? For example, Glory to God is a song of praise, and some music at Communion will be more reflective.
One must consider different styles of music, such as devotional music, traditional, or contemporary. At the same time, many of these types of music are more fitting for a devotional context rather than at Mass. Musically, the text must be appropriate, singable, and not at the exclusion of the liturgical assembly. From a pastoral point of view, the assembly and age group must be considered.
Much also depends on the resources available – who can do what and to what standard? There is a repertoire for an organ and four part choir, another for a music group with or without a keyboard. In any event, do what you can, not what you can’t! Sometimes doing less but doing it well is the answer.
Lastly, there should be a unity of musical style, to keep with the unity of the liturgical celebration. All of this should be in the context of prayer. Please see the General Instruction of the Roman Missal 39-41 for further information.
