Yes rest days are important because your body needs to recover. I have to share this article about the importance of rest days and how it helps in your recovery and weight loss.
Rest days should be ‘active rest’ days so not just laying around not doing anything. You still need to get up and moving. Walking, yoga, or a jog depending on how hard you train. This article sums it up in an easy to understand manner that I don’t think I could describe any more clear.