He wants you to learn to play offense on defense. To attack the baseball. To "work to and through the baseball." When your in your pre stance and creeping on the pitch the only time you should ever field a ball that your not playing through is when it is totally ripped right at you and you don't have any time to play through it. You either reach out and glove it, back hand it, or fore hand it.
When you do have time to play through a baseball which is going to be the vast majority of opportunities your footwork and approach is one that allows you to play through the baseball and work towards your target. This not only puts you in the best fielding position to make a play, its much quicker and sets up your throw. It allows you to play athletic baseball, offense on defense, attacking the baseball.
The whole goal is to create momentum towards your target before you field the baseball. This is impossible when a ball is smoked right at you. But it doesn't matter because you have time to create that "Mo" because its smoked right at you. I call that "Neutral Mo." There are two other types of "Mo" when fielding a GB. Positive and Negative. An example of Positive Mo would be a GB to the glove side of the SS and the play is at 2B. The approach to the baseball is taking you towards the throw. Thats good. Then an example of negative "MO" would be a GB to your throwing hand at 2B and your throw is at 1B. The proper athletic approach can negate that negative "MO" and in some cases still allow you to create positive "MO" towards the throw.
In other words to not squat on GB's. Do not play stationary. Attack the baseball creating positive momentum towards your target on the approach. As you move up in the game and runners are faster and really get out of the box, as the game speeds up you will not be able to compete. You will be in poor throwing positions because of your poor approach. There are many drills to help with this. I could type for days on this topic.