That it might be fulfilled - This is taken from Psalms 78:2-3. The sense, and not the very words of the Psalm, are given. Christ taught, as did that prophet - Asaph - in parables. The words of Asaph described the manner in which Christ taught, and in this sense it could be said that they were fulfilled. See the notes at Matthew 1:22-23.
Related Commentaries of Matthew 13:34
Matthew 13:34-35
34 All these things spake Jesus unto the multitude in parables; and without a parable spake he not unto them:
35 That it might be fulfilled which was spoken by the prophet, saying, I will open my mouth in parables; I will utter things which have been kept secret from the foundation of the world.