Depending on your training routine rest days are imperative to progress. The body is not built for the continuous stress of full on training.
Rest is also relative, depending on the intensity of training sometimes a rest day can just mean light Randori or Kata practice:
When training for bigger competitions you typically increase your training input, reaching maximum intensity about a week before the competition, then rest by only taking very light training to keep the body supple, reduce the risk of injury and let the body recover and build strength. Often with no training whatsoever on the last day or two. After a rest you will almost certainly notice that things suddenly come together a lot easier and that one technique that you have practiced for weeks and just could not get, now magically works.
I assume your trainer knows what he is doing and has noticed something in your training that suggest you need to take it a bit easier for a couple of days. This is a very positive sign of a good trainer.
all the best