Rest and recovery are as necessary for muscle-building as exercise.
This is because of the way muscle building actually works. During exercise, muscles are strained and tiny tears occur in the muscle fibers.
Then, while you’re resting, your body fixes the tears and builds the muscles up more than before in order to ensure they can handle the strain that you put on them.
Because rest and recovery are so important, there is a right and wrong way to do it.
If you’re not focusing on recovery and just doing nothing but exercising for muscle-building, then there’s a good chance that you’re not going to see the results that you want.