"In the earlier part of His ministry, Christ had spoken to the people in words so plain that all His hearers might have grasped truths which would make them wise unto salvation. But in many hearts the truth had taken no root, and it had been quickly caught away. “Therefore speak I to them in parables,” He said; “because they seeing see not; and hearing they hear not, neither do they understand.... For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed.” Matthew 13:13-15 . COL 20.2"
"Therefore speak I to them in parables: because they seeing see not; and hearing they hear not, neither do they understand. And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive: For this people’s heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes, and hear with their ears, and should understand with their heart, and should be converted, and I should heal them."
Ellen White directly references Matthew 13:13-15 in this passage.
"Jesus desired to awaken inquiry. He sought to arouse the careless, and impress truth upon the heart. Parable teaching was popular, and commanded the respect and attention, not only of the Jews, but of the people of other nations. No more effective method of instruction could He have employed. If His hearers had desired a knowledge of divine things, they might have understood His words; for He was always willing to explain them to the honest inquirer. COL 20.3"
"And the disciples came, and said unto him, Why speakest thou unto them in parables?"
The EGW passage explains Jesus's use of parables to awaken inquiry and impress truth, which is directly related to the disciples' question in Matthew 13:10 about why Jesus spoke in parables.