Matthew 5:1-2 states
Seeing the crowds, Yeshua walked up the hill. After he sat down,his talmidim came to him, and he began to speak. This is whathe taught them (CJB).
Matthew juxtaposes the disciples with the crowds as he presents the Sermon on the Mount. Matthew here makes clear that the sermon is for disciples. The disciples gathered to him and he taught them. This perspective is of course born out through a study of the sermon. It is important to point out that at this stage in Matthew’s narrative the disciples are not yet identified as the Twelve. This will happen later in Matthew 10. So the disciples here are different than the crowd, but not yet the Twelve. Interestingly, after chapter 10 when Matthew uses the term disciples it is equivalent to the Twelve.
Yet, while the sermon is for the disciples it is in earshot of the crowds. The crowds while not the direct recipients of the message are nevertheless hearing the message. This point should not be too quickly passed over. The question deserves to be deeply reflected on: What might the juxtaposition of the “crowds” with the “disciples”, to whom Jesus message is directed, mean for how the church engages with the world? At the very least, it means that our message to ourselves should not be whispered in a corner. The “crowds” must overhear the message of the nature of discipleship. Discipleship is not a tag on after one comes to faith in Jesus. The uncompromising message of discipleship is to be heard by those on the outside.
Perhaps we as a western church in the late 20th and early 21st century have been far to concerned not to offend or unnecessarily confuse the "basic" message of the Gospel with teaching on the life of discipleship.