What is the purpose of a Sermon?

I'm spending some time interacting with neighboring blogs before continuing some of my own series. Today I wanted to consider an issue raised at Conciliar Outpost about an Anglican's view of the purpose of a sermon. I'd encourage people to read the whole linked article but will sum up here enough for those who only read this continuation of the conversation. The linked post sees three main types of sermons as problems to be avoided: the moral to-do list, the call to social action (generally as political activism), and the academic lecture. It advocates this as the correct content of a sermon: 

The sermon is the preaching of Gospel to the congregation in a way that convicts them of sin while also preparing them for the Eucharist. A Lutheran may call this “Law/Gospel” preaching. There is a sense in which the sermon should destroy self-confidence in the hearer while also pointing them to the crucified Lord.

To be clear, the context is in a liturgical worship service, where the sermon is part of the bridge between reading 3 portions of Scripture -- the third of which is from one of the New Testament gospels -- and the Eucharist or Lord's Supper.

Again to be clear, I'm not writing this from any adversarial view of Anglicans or Lutherans.

But is that really what a sermon should be? Is there a one-size-fits-all answer to what a sermon should be, other than a faithful conveyance of the Word of God? The sermon should be faithful to the text being preached. What if the scripture reading for the day isn't intended to convict people of sin? How can it be faithful to the Scripture to insist that every sermon should serve to convict of sin when every scriptural reading does not? The sermon should serve as a means by which the shepherd feeds the sheep, as "Man does not live on bread alone, but by every word which comes from the mouth of the Lord."

The purpose of the sermon should be much the same as the purpose of the Scripture itself. In addition to the things already named, I can think of Scripture passages which also include the following among the right things accomplished by God's word:

• Building faith
• Encouragement
• Gaining wisdom and understanding
• Giving joy
• Increasing knowledge of God
• Renewal and regeneration
• Comforting and strengthening God's people

 I expect there are many more. I'd be glad to hear of others.