Clearly =
In a way that is easy to see, hear, read, or understand.
The Scriptures =
"Then He opened their minds so they could understand the Scriptures."
Opened =
dianoigō =
To open by dividing or drawing asunder, to open thoroughly (what had been closed).
Of the eyes and the ears.
To open the mind/ to cause to understand.
To rouse in one the faculty of understanding.