Adam Clarke on Luke 24:45

Then opened he their understanding - Διηνοιξεν, He fully opened. They had a measure of light before, so that they discerned the Scriptures to be the true word of God, and to speak of the Messiah; but they had not light sufficient to enable them to apply these Scriptures to their Lord and Master; but now, by the influence of Christ, they see, not only, the prophecies which pointed out the Messiah, but also the Messiah who was pointed out by these prophecies. The book of God may be received in general as a Divine revelation, but the proper meaning, reference, and application of the Scriptures can only be discerned by the light of Christ. Even the very plain word of God is a dead letter to those who are not enlightened by the grace of Christ; and why? because this word speaks of spiritual and heavenly things; and the carnal mind of man cannot discern them. They who receive not this inward teaching continue dark and dead while they live.