35 That the intimate connection between words and rites may be apparent in the liturgy: 1) In sacred celebrations there is to be more reading from holy scripture, and it is to be more varied and suitable. 2) Because the sermon is part of the liturgical service, the best place for it is to be indicated even in the rubrics, as far as the nature of the rite will allow; the ministry of preaching is to be fulfilled with exactitude and fidelity. The sermon, moreover, should draw its content mainly from scriptural and liturgical sources, and its character should be that of a proclamation of God's wonderful works in the history of salvation, the mystery of Christ, ever made present and active within us, especially in the celebration of the liturgy. 3) Instruction which is more explicitly liturgical should also be given in a variety of ways; if necessary, short directives to be spoken by the priest or proper minister should be provided within the rites themselves. But they should occur only at the more suitable moments, and be in prescribed or similar words. 4) Bible services should be encouraged, especially on the vigils of the more solemn feasts, on some weekdays in Advent and Lent, and on Sundays and feast days. They are particularly to be commended in places where no priest is available; when this is so, a deacon or some other person authorized by the bishop should preside over the celebration.
Source: Sacrosanctum Concilium (Vatican.va)