Hebrews 5:11

“In fact, though by this time you ought to be teachers, you need someone to teach you the elementary truths of God’s word all over again. You need milk, not solid food!”

Immediately follows and elaborates on the difficulty in explaining deeper truths.

“Brothers and sisters, I could not address you as people who live by the Spirit but as people who are still worldly—mere infants in Christ. I gave you milk, not solid food, for you were not yet ready for it. Indeed, you are still not ready. You are still worldly.”

Parallel imagery of milk and solid food representing spiritual maturity.

“Therefore let us move beyond the elementary teachings about Christ and be taken forward to maturity, not laying again the foundation of repentance from acts that lead to death, and of faith in God.”

Continues the theme of spiritual maturity and moving beyond basic teachings.

“In them is fulfilled the prophecy of Isaiah: “ ‘You will be ever hearing but never understanding; you will be ever seeing but never perceiving. For this people’s heart has grown callous; they hardly hear with their ears, and they have closed their eyes. Otherwise they might see with their eyes, hear with their ears, understand with their hearts and turn, and I would heal them.’”

Relates to the difficulty in understanding spiritual truths due to a lack of spiritual receptiveness.

““I have much more to say to you, more than you can now bear.”

Illustrates the principle that some truths are difficult to grasp depending on the hearer's capacity.