There is always a gap between our words and our thoughts, but Jesus' words perfectly represent his thinking. He never had to correct himself or explain what he "meant" to say. Whoever hears Jesus' words hears him. His words perfectly express his convictions; they also represent his character. His thought, his character, and his actions are wholly consistent. If we follow his word, we become like him, and that is a blessed thing (Matt. 5:3-12). That is another reason to accept the authority of his every word (7:28).
The clarity and power of Jesus' teaching is stirring, yet alarming because honest people know they cannot obey it. Some believe that it is also impractical, since it calls disciples to turn the other cheek and to give to all who ask, and these are hardly strategies calibrated for survival in a rough world. Taking the beauty, the authority, and the rigor together, it is no wonder that the church struggles to interpret the Sermon on the Mount.
Daniel Doriani in The Sermon on the Mount: The Character of a Disciple