The first two movements in today's shoulder and ab workout make perfect sense as partner-assisted exercises. If you've been lifting for a few years, you've probably gotten help on shoulder presses or lateral raises at one point or another, and you know how beneficial a pair of hands guiding your elbows up can be.
The final exercise today, however, asks you to provide a different sort of assistance—the competitive kind. It's a farmer's-carry competition, meaning you each pick up a single dumbbell—preferably the same weight, but that may not be the case for some partners—and see who can carry it for the longest time. You may think that sounds like an intense grip challenge, and you're right, but your grip definitely won't be the only thing getting taxed. Get ready to feel your abs and upper back tomorrow in addition to your forearms.
By the end of this week, you won't necessarily see physical changes. You won't see this great aesthetic body of the future taking shape in the mirror. But you will feel something: extreme soreness. You will feel drained after each workout, and you'll be ready for your weekend off.
You've put in a really solid work week with great effort, and the reward is soreness for now. Expect that, eat up, and move on to Week 2.