V. Sacred Music in the Celebration of the Sacraments and Sacramentals, in Special Services of the Liturgical Year, etc.
42. The Council has stated as a principle that whenever rites according to their specific nature make provision for communal celebration involving the presence and active participation of the faithful, this way of celebrating them is to be preferred to a celebration that is individual and, so to speak, private.  From this it follows that singing becomes very important, in that it more strikingly expresses the "ecclesial" aspect of celebration.
43. Certain celebrations of the sacraments and sacramentals are particularly significant in the life of a parish community: confirmations, ordinations, marriages, the consecration of a church or altar, funerals, etc. As far as possible, therefore, they should be carried out with singing, so that even the solemnity of the rite may contribute to a greater pastoral effectiveness. Every precaution is to be taken, however, against introducing into a celebration under the guise of solemnity anything merely profane or out of keeping with divine worship; this applies particularly to marriages.
44. Celebrations that have a distinctive character in the course of the liturgical year should also be marked by greater solemnity through singing. The rites of Holy Week should be given a unique solemnity; through the celebration of the paschal mystery these rites lead the faithful to the very center of the liturgical year and of the liturgy itself.
45. Suitable melodies are also to be provided for the liturgy of the sacraments and sacramentals and for other special services of the liturgical year. These melodies are meant to favor a more solemn celebration even in the vernacular, in keeping with the norms of the competent authority and the capability of each liturgical assembly.
46. Music also has great power to nurture the faithful's devotion in celebrations of the word of God and in popular devotions.
The model for celebrations of the word of God  should be the liturgy of the word at Mass.  Among the important resources for popular devotions are the psalms, musical works taken from the treasury of the past and the present, the religious songs of the people, the playing of the organ and other suitable instruments.
Musical pieces that no longer have a place in the liturgy, but have the power to touch religious feeling and to assist meditation on the sacred mysteries are very well suited for use in popular devotions and especially in celebrations of the word of God.