A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
deu 8:1AN EXHORTATION TO OBEDIENCE. (Deu. 8:1-20)
All the commandments which I command thee this day shall ye observe to do, that ye may live--In all the wise arrangements of our Creator duty has been made inseparably connected with happiness; and the earnest enforcement of the divine law which Moses was making to the Israelites was in order to secure their being a happy (because a moral and religious) people: a course of prosperity is often called "life" (Gen 17:18; Pro 3:2).
live, and multiply--This reference to the future increase of their population proves that they were too few to occupy the land fully at first.
deu 8:2thou shalt remember all the way which the Lord thy God led thee these forty years in the wilderness--The recapitulation of all their checkered experience during that long period was designed to awaken lively impressions of the goodness of God. First, Moses showed them the object of their protracted wanderings and varied hardships. These were trials of their obedience as well as chastisements for sin. Indeed, the discovery of their infidelity, inconstancy, and their rebellions and perverseness which this varied discipline brought to light, was of eminently practical use to the Israelites themselves, as it has been to the church in all subsequent ages. Next, he enlarged on the goodness of God to them, while reduced to the last extremities of despair, in the miraculous provision which, without anxiety or labor, was made for their daily support (see on Exo 16:4). Possessing no nutritious properties inherent in it, this contributed to their sustenance, as indeed all food does (Mat 4:4) solely through the ordinance and blessing of God. This remark is applicable to the means of spiritual as well as natural life.
deu 8:4Thy raiment waxed not old upon thee, neither did thy foot swell, these forty years--What a striking miracle was this! No doubt the Israelites might have brought from Egypt more clothes than they wore at their outset; they might also have obtained supplies of various articles of food and raiment in barter with the neighboring tribes for the fleeces and skins of their sheep and goats; and in furnishing them with such opportunities the care of Providence appeared. But the strong and pointed terms which Moses here uses (see also Deu 29:5) indicate a special or miraculous interposition of their loving Guardian in preserving them amid the wear and tear of their nomadic life in the desert. Thirdly, Moses expatiated on the goodness of the promised land.
deu 8:7For the Lord thy God bringeth thee into a good land--All accounts, ancient and modern, concur in bearing testimony to the natural beauty and fertility of Palestine, and its great capabilities if properly cultivated.
a land of brooks of water, of fountains and depths that spring out of valleys and hills--These characteristic features are mentioned first, as they would be most striking; and all travellers describe how delightful and cheerful it is, after passing through the barren and thirsty desert, to be among running brooks and swelling hills and verdant valleys. It is observable that water is mentioned as the chief source of its ancient fertility.
deu 8:8A land of wheat, and barley--These cereal fruits were specially promised to the Israelites in the event of their faithful allegiance to the covenant of God (Psa 81:16; Psa 147:14). The wheat and barley were so abundant as to yield sixty and often an hundredfold (Gen 26:12; Mat 13:8).
vines, and fig trees, and pomegranates--The limestone rocks and abrupt valleys were entirely covered, as traces of them still show, with plantations of figs, vines, and olive trees. Though in a southern latitude, its mountainous formations tempered the excessive heat, and hence, figs, pomegranates, &c., were produced in Palestine equally with wheat and barley, the produce of northern regions.
honey--The word "honey" is used often in a loose, indeterminate sense, very frequently to signify a syrup of dates or of grapes, which under the name of dibs is much used by all classes, wherever vineyards are found, as a condiment to their food. It resembles thin molasses, but is more pleasant to the taste [ROBINSON]. This is esteemed a great delicacy in the East, and it was produced abundantly in Palestine.
deu 8:9a land whose stones are iron--The abundance of this metal in Palestine, especially among the mountains of Lebanon, those of Kesraoun, and elsewhere, is attested not only by JOSEPHUS, but by Volney, Buckingham, and other travellers.
brass--not the alloy brass, but the ore of copper. Although the mines may now be exhausted or neglected, they yielded plenty of those metals anciently (Ch1 22:3; Ch1 29:2-7; Isa 60:17).
deu 8:11Beware that thou forget not the Lord--After mentioning those instances of the divine goodness, Moses founded on them an argument for their future obedience.
deu 8:15Who led thee through that great and terrible wilderness, wherein were fiery serpents, and scorpions--Large and venomous reptiles are found in great numbers there still, particularly in autumn. Travellers must use great caution in arranging their tents and beds at night; even during the day the legs not only of men, but of the animals they ride, are liable to be bitten.
who brought thee forth water out of the rock of flint--(See on Deu 9:21).