The 1967 document "Musicam sacram", that implemented the Constitution on the Sacred Liturgy after the Second Vatican Council, repeatedly mentions facilitating the full, active participation of the congregation as called for by the Council. so that "unity of hearts is more profoundly achieved by the union of voices. "Musicam Sacram" states: "One cannot find anything more religious and more joyful in sacred celebrations than a whole congregation expressing its faith and devotion in song. Therefore the active participation of the whole people, which is shown in singing, is to be carefully promoted." It calls for fostering this congregational participation through attention to choice of song directors, to choice of songs, and to the nature of the congregation. It mentions the duty to achieve this participation on the part of choirs, choirs directors, pastors, organists, and instrumentalists. To achieve full, active participation of the congregation, great restraint in introducing new hymns has proven most helpful. To this end also, the General Instruction of the Roman Missal recommends use of "seasonal" responsorial psalms and also keeping to a song that all can sing while processing to Communion, to “express the communicants’ union in spirit by means of the unity of their voices, to show joy of heart, and to highlight more clearly the ‘communitarian’ nature of the procession to receive Communion.”