In the Apollo lunar missions, two astronauts descended to the lunar surface in the Lunar Excursion Module (LEM) while one astronaut stayed onboard the Apollo capsule orbiting the moon.
The Orion CEV will carry four astronauts to the moon and all four will descend to the lunar surface while the empty Orion orbits the moon under robotic control. That doubles the man-hours of work and exploration possible on the lunar surface.
Furthermore, the Orion CEV will be designed to support missions up to six months long eventually.
Then they'll have to make a new ship for traveling to Mars, and it'll have to have stronger shielding from radiation, too. Even from a solar flare.