Albert Barnes Commentary Matthew 13:34-35

"All these things spake Jesus in parables unto the multitudes; and without a parable spake he nothing unto them: that it might be fulfilled which was spoken through the prophet, saying, I will open my mouth in parables; I will utter things hidden from the foundation of the world." — Matthew 13:34-35 (ASV)

That it might be fulfilled. This is taken from Psalm 78:2-3. The sense, and 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 Barnes on Matthew 1:22-23.