The Scribes and Pharisees had been placed in a position of care over God’s people but had abused that position for their own benefit. Jesus tells them a parable to bring this home to them - indicating that they were liable to condemnation and judgment for their sins.
Christ likened himself to a stone which, if people did not receive Him, would ultimately fall on them in judgment.
This passage is applied to the elders of the church first, as those who now have responsibility over God’s people. Then application is made to all people - what have we done with Christ? Are we liable to judgment for rejecting Him? If we have come to know Christ, are we doing all we can to make Him known to others?