This rest was needed because one did not even have time to eat in the enormous busyness of the people’s coming and going around Jesus. This explanatory addition (Mark 6:31b) makes clear that the withdrawal is not made because it would be a burden to look after the people, but in order to ensure that they can continue their work among them. This rest is not a goal, but a means for work. Therefore, it is also “for a while” only: after that the Twelve may continue their work in Israel with Jesus.1
31 And he said to them, “Come away by yourselves to a desolate place and rest a while.” For many were coming and going, and they had no leisure even to eat.