The incident that Mark recorded in Mark 12:28-34 is quite similar to this one, but the differences in the accounts point to two separate situations. In view of the question at stake it is easy to see how people might have asked it of Jesus many different times. Furthermore this particular question was of great concern to the scribes, who studied the law professionally. The fact that the Holy Spirit recorded the same lesson twice in Scripture is a testimony to His greatness as a teacher since great teachers deliberately repeat themselves. [source][source][source]
". . . in the first century A.D. in Palestine the only way of publishing great thoughts was to go on repeating them in talk or sermons." [1][source]