I'm listening to Dan Carlin's blueprint for Armageddon podcast and one thing he never addressed is why the German second army was en route and drawing nearer to Paris but then changes course and moves east of Paris a few days before the First battle of Marne? I wouldn't mind a simple or short answer as its a short question.

I'm wondering this because the Second army moving east was basically the reason the battle of Marne was given an opportunity to work.