Surprisingly, the young man's gaze focuses on something else - something we do not see - and not the prayer book in his hand. Has something distracted him?
Though he is not reading the text, he seems to be imagining something happening before him, or rather, inside him?
Another important feature of Devotio Moderna was the ability to transform the physical image into a visual image in the mind. This act was important in the spiritual journey as it brought the individual closer to Christ.
This 'unfocused gaze' can be seen in other paintings from the period. On the left is an example of one of Hans Memling's portraits featuring this outward gaze as the sitter is engaged in spiritual contemplation.