This is a text effect that shows a portion of the text focusing in and out as the cursor moves over it. It was designed by Jonny Scholes. A similar effect of scanning the text is seen here.
If you are having trouble with the pen, try the archived copy on GitHub
Focus In/Out Snippet
See the Pen In/out of focus text effect by Jonny Scholes (@jonnyscholes) on CodePen.0