Then follows the book of Leviticus, in which the precepts bearing upon sacrifice are set forth; commandments also are added to the law formerly given; and almost the whole is full of instructions connected with the priests. If any one wishes to become acquainted with these, he will obtain fuller information from that source. For we, keeping within the limits of the work undertaken, touch upon the history only. The tribe of Levi, then, being set apart for the priesthood, the rest of the tribes were numbered, and were found to amount to six hundred and three thousand five hundred persons. When, therefore, the people made use of the manna for food, as we have related above, even amid so many and so great kindnesses of God, showing themselves, as ever, ungrateful, they longed after the worthless viands to which they had been accustomed in Egypt.
Then the Lord brought an enormous supply of quails into the camp; and as they were eagerly tearing these to pieces, as soon as their lips touched the flesh, they perished. There was indeed on that day a great destruction in the camp, so that twenty and three thousand men are said to have died. Thus the people were punished by the very food which they desired. Thence the company went forward, and came to Faran; and Moses was instructed by the Lord that the land was now near, the possession of which the Lord had promised them.
Spies, accordingly, having been sent into it, they report that it was a land blessed with all abundance, but that the nations were powerful, and the towns fortified with immense walls. When this was made known to the people, fear seized the minds of all; and to such a pitch of wickedness did they come, that, despising the authority of Moses, they prepared to appoint for themselves a leader, under whose guidance they might return to Egypt. Then Joshua and Caleb, who had been of the number of the spies, rent their garments with tears, and implored the people not to believe the spies relating such terrors; for that they themselves had been with them, and had found nothing dreadful in that country; and that it behooved them to trust the promises of God, that these enemies would rather become their prey than prove their destruction.
But that stiff-necked race, setting themselves against every good advice, rushed upon them to destroy them. And the Lord, angry on account of these things, exposed a part of the people to be slain by the enemy, while the spies were slain for having excited fear among the people.
Source: Sacred History (New Advent)