The classic Anglican book, Liturgy and Worship (SPCK, ed. Clarke and Harris), has a great chapter on liturgical silence, and discusses it in the context Holy Eucharist. Originally the entire eucharistic liturgy was recited audibly, but at a rather early date, in both and west, the most solemn parts of the liturgy began to be said softly or silently. It was meant to evoke a certain sense of awe and mystery in the worshipper. Various church fathers, such as Cyril of Jeruslam, spoke on this topic. The offering of the eucharist was, according to Cyril, the "greatest hour of trembling", so naturally the tone of the liturgy, and how it was said, began to express this.
Anyone who has done even a little bit of public speaking knows that changing your tempo, tone, and volume are very powerful communication tools. That is what all of the great preachers have done (e.g. just watch a classic Billy Graham sermon from the 50's on TV sometime). So naturally one would do that at the liturgy in appropriate ways. It can also be a pedagogical tool. I was trained to say the Words of Institution softly, but I must confess I like the practice of the clergy of the parish I attended in seminary better, where they said those words loudly and with clarity, in order to emphasize, I think, the Real Presence.
The first time I heard him say those words in that way I knew that he believed in the Real Presence.
Related to this is the whole problem of rushing through the liturgy and not saying the silent prayers in the missal because people find the silences "awkward". Personally, I think they need to just get over that. Silence is the most undervalued thing in the world (besides my art). When we sit through those longish pauses in the liturgy, it helps us slow down and really concentrate on what is happening so we can be more involved in the sacred action, and get more out of it. I think that our churches would be even more reverent and holy places if we sought to slow things down a bit and learned to observe and appreciate the periods of silence and quiet in our worship.
