John Wesley on Mark 6:9

Be shod with sandals - As you usually are. Sandals were pieces of strong leather or wood, tied under the sole of the foot by thongs, something resembling modern clogs. The shoes which they are in St. Matthew forbidden to take, were a kind of short boots, reaching a little above the mid - leg, which were then commonly used in journeys. Our Lord intended by this mission to initiate them into their apostolic work. And it was doubtless an encouragement to them all their life after, to recollect the care which God took of them, when they had left all they had, and went out quite unfurnished for such an expedition. In this view our Lord himself leads them to consider it, Luke 22:35: When I sent you forth without purse or scrip, lacked ye any thing?