Here is a great post from Alastair Roberts of Scotland:

Liturgy is so important, precisely as borrowed language. People complain about praying someone else’s words rather than their own in the liturgy, but that is the precise point of liturgy. By ‘borrowing’ the language of the Church which has been handed over to us (in tradition) we hand ourselves over to God and to each other (Peter Candler explores this well in his latest book).
The ‘heroic pose’ that Keillor speaks of is one in which the speaker presents God with his own words, deeming his own vocabulary to be sufficient. The reasoning behind such an approach is that the most authentic way of being is that of spontaneity as opposed to imitation. Prayers of spontaneity, no matter how rhetorically brilliant they are, will always fall short of truly public speech. True public speech is shared language, where the words are not the speaker’s own. Spontaneous speech always falls short, drawing attention to the speaker, who often has a desire for people’s praise.The language of liturgy is public language, precisely because it does not belong to any one particular individual. It has been handed over to all of us and we are given to participate in it. Such language has a pedagogical purpose. As Candler puts it: ‘To enter into this pedagogy is to entrust oneself to a language which is not one’s own, yet which transforms one’s language and orders it to God.’ Such language is a gift and not our own possession.

This is one of the reasons why the book of Psalms and things such as the Lord’s Prayer should be central in our worship. The psalms and the Lord’s Prayer are words that God has given to us. They are words that we ‘borrow’. As we ‘borrow’ these words we are participating in the inspired speech of the Holy Spirit, which will serve to reform all of our language. Such participation in borrowed language transforms us and redeems our speech. It should be regarded as having a salvific and not merely a bare pedagogical purpose. Brian Daley puts it well: ‘The Psalms … do not simply command us to repent of our sins, to bear suffering patiently, or to praise God for his gifts; they actually give us the words by which we can say and do these things for ourselves.’ In handing ourselves over to a language that has been handed over to us in tradition we confess that we do not have the words that are sufficient to approach God. Our verbal works are sinful and poor, so they are not the sacrifice of praise our tongues present to God. The words that we bring are words that have been given to us, words that are not our own. The shared language of liturgy is thus a natural extension of the doctrine of justification by faith alone.
When we strive for spontaneity in speech and resist faithful imitation we also fail to hand ourselves over to each other. Worship ceases to be truly public and gradually reduces to the voices of many individuals expressing their private spirituality in front of others. Our private spirituality becomes something of public show. Whether we intend to receive praise from other men or not, private prayer belongs in the private place. When it is brought into the public place it can easily draw attention to the one who prays and away from the One to whom the prayer is addressed. Public prayer is not to be the creation of individual rhetorical brilliance, but the gift of shared speech. The loss of robust liturgies and the rise of individual rhetoric would also seem to have had some effect in the rise of individualistic understandings of the Christian faith. Lacking a shared language we have not handed ourselves over to each other. Our spirituality is a ‘heroic’ spirituality; a spirituality of me and Jesus, without the need for any other.Within evangelicalism our worship services are primarily about our own speech. The focus of the service is not on the shared language of the liturgy, but on the words of the preacher. It is the preacher who composes the words of the sermon and the words of the prayers. Consequently, the person of the preacher becomes far more central than the priest ever became within medieval Catholicism. In the case of medieval Catholicism it was the office of the priest that became central. However, as the language and rituals performed by the clergy were ‘borrowed’, it was not the priest as a particular person that became central. Within modern evangelicalism it is the pastor (or — heaven help us — the worship leader) that becomes central as a particular person and not merely as an office. Churches become centred on a particular person in a way that is deeply unhealthy.One of the things that the Church could really benefit from today is a downplaying of preaching within the context of the liturgy and a denial of the primacy of the preacher. The pastor need not stand to teach (although we ought to stand for the reading of the Scriptures); he is not engaging in a rhetorical display. All he needs to do is explain the passage in simple language and make some applications. Under such teaching people will have their lives informed by God’s Word, without the personality of the preacher becoming central (as it tends to do in, for example, the Spurgeon style of preaching). A further thing that is important is to retain the primacy of the reading of Scripture. The sermon is in service of the read Scripture, rather than vice versa. The reading of the Scriptures should not merely consist of the passage that the preacher has chosen for his message.The relationship between the sermon and the reading of the Scriptures is not unimportant. It will train congregations in their relationship to the Scriptures. Preachers who always choose their own passages can train congregations (in more ways than one) to be people who choose their own passages too and do not submit to the Scriptures as a whole. Pastors who choose Scripture readings purely on the basis of what they want to say, should not be surprised if their congregations become the sort of people who merely trawl the Scriptures for devotional nuggets and never learn to be attentive and receptive to the Scriptures. Having set readings of Scripture trains us to submit to a language other than our own, rather than merely appropriating the language of the Scripture in service of our own speech. Set readings that challenge and unsettle pastors are important. They save us from becoming glib. Congregations who witness their pastor silenced or confused by the set Scripture will learn an important lesson about the relationship between the Church and Scripture, even if they don’t come away understanding the passage itself.