{They were astonished} (exepl(8873)sonto). Pictorial imperfect
as in  Lu 4:32  describing the amazement of the audience,
"meaning strictly to strike a person out of his senses by some
strong feeling, such as fear, wonder, or even joy" (Gould). {And
not as their scribes} (kai ouch h(9373) hoi grammateis).  Lu 4:32 
has only "with authority" (en exousi(8369)). Mark has it "as having
authority" (h(9373) ech(936e) exousian). He struck a note not found by
the rabbi. They quoted other rabbis and felt their function to be
expounders of the traditions which they made a millstone around
the necks of the people. By so doing they set aside the word and
will of God by their traditions and petty legalism ( Mr 7:9,13 ).
They were casuists and made false interpretations to prove their
punctilious points of external etiquette to the utter neglect of
the spiritual reality. The people noticed at once that here was a
personality who got his power (authority) direct from God, not
from the current scribes. "Mark omits much, and is in many ways a
meagre Gospel, but it makes a distinctive contribution to the
evangelic history _in showing by a few realistic touches_ (this
one of them) _the remarkable personality of Jesus_" (Bruce). See
on  Mt 7:29  for the like impression made by the Sermon on the
Mount where the same language occurs. The chief controversy in
Christ's life was with these scribes, the professional teachers
of the oral law and mainly Pharisees. At once the people see that
Jesus stands apart from the old group. He made a sensation in the
best sense of that word. There was a buzz of excitement at the
new teacher that was increased by the miracle that followed the
sermon.