Who is the Sermon on the Mount preached to? What is the intended audience?
Matthew 5:1 indicates that the disciples are the main audience. Jesus takes his seat on the mountain, waits for his disciples to join him, and then opens his mouth to teach them. That means the demands Jesus makes are for his followers. This is kingdom ethics, gospel ethics - not a general ethic for the world at large. That makes sense - as far as Matthew is concerned, the teaching in the Sermon is part and parcel of the preaching of the gospel. (Note the parallelism of teaching and proclaiming in 4:23). So we shouldn't expect this ethical discourse to be immediately applicable to everyone.
On the other hand, 7:28 indicates that the crowds heard Jesus' teaching, and reacted with astonishment. Doubtless this is deliberate on the part of Jesus - he is very capable of taking the disciples aside for private teaching when he wants to. Again, the preaching of this way of life is part of the preaching of the gospel. It is meant to be attractive (or repellent!) to the curious spectator. Like the gospel generally, it either draws people in or drives them away. This also has the effect of making it possible for people to measure the disciples' conduct against Jesus' ideal. No doubt this too is deliberate and planned. My lifestyle is meant to preach.
Probably the last group I'd want to mention weren't part of Jesus' audience originally, but they could be part of Matthew's (and therefore of Jesus' secondarily). I mean the hypocrites the Sermon makes regular mention of. They probably weren't on the mountain to hear their condemnation. But now as we read the Sermon we are invited to ensure that we are not in this latter group.
Where am I today? Following, spectating, play-acting?