Genesis 18:5

and I will fetch a morsel of bread; and comfort ye your hearts. After that ye shall pass on; for therefore are ye come to your servant. The entire invitation of Abraham shows that this was not a case of ordinary hospitality to passing strangers, but a work of love performed for the Lord. He wanted the favor of the Lord, of which he was sure by reason of the covenant, to abide with him; hence the urgency of the prayer. There is nothing lacking in the cordial nature of the invitation: Let a little water be taken, and wash your feet. The sandals of the travelers having been removed, the house-slaves provided the water for washing off the dust. Under the tree they were then to recline, resting upon their arms as supports, while Abraham hurried to have dinner prepared, the principal meal being eaten at noon, 1 Kings 20:16. He spoke in a deprecating way of the small meal which he was able to offer them: a bit of bread. Yet he hoped that what he had to offer would be sufficient to refresh their hearts before continuing their journey. Thus the assurance that their entertainment would cause neither trouble nor expenditure was intended to remove any hesitation about accepting his hospitality. And they said, So do as thou hast said. They did not want him to go to any trouble; they accepted only with the condition that he would serve but a simple repast.