What Mobster means by that, Ste Moldovski, is that our bodies need rest and thus recovery because that is when our bodies - to wit, our muscles - grow. Indeed, our bodies grow primarily while we are sleeping.
Training, on the other hand, breaks down our muscles, thereby actually making them smaller. Therefore, if one were train every day, then one's body would never grow. So rest and enjoy it.
actually you need to train less if you wanna bulk up fast because you will burn too many calories working out eveyrday and your muscles wont grow but can actually even become smaller from overtraining. You wanna train 3 times a week (maximum 4) no longer then 1 hour each time. You grow when you eat not when you train, there as a quote, better to miss a workout then a meal