Mr. Covey goes on here to say that if you improve upon/renew any of the four dimensions that make up your being that dimension will have a positive effect on the others as well. So by focusing on the renewal of all four dimensions is going to create a sum result that is greater than all of its parts!
The same holds true for The 7 Habits of Highly Effective People. Covey tells us that we cannot improve in one of the seven habits without improving, at least in part, one or two others. So if one improves in all seven the end result is something that is far more synergistic in nature.