Deuteronomy 33:25

The mighty men of Israel would dwell in the border towns and lock the frontier so no enemies could enter; it was as if it were closed with locks and bars of iron and brass

The tribe of Asher be sound as iron, and their feet-strong as brass in walking on the stony rocks; and as the days of their youth so shall they be strong in their age.

Your doorbolts are iron and brass because there will be hills of iron and brass in his territory.

as your days is your strength The latter word has no cognate, although the meaning of the Aramaic translation [“may your old age be like your youth”] is well known (that you will have vigor all your life). There are some who say that the ’ alef in this word [Hebrew: dov ekha] takes the place of the duplicated letter in an ‘ayin-‘ayin root (as it does in “whose land the rivers have despoiled” [Isaiah 18: 2]), thus relating the word to “causing the sleepers’ lips to murmur [Hebrew: dovev]” [Song of Songs 7: 10]. But this idea is nonsense.

IRON AND BRASS SHALL BE THY BARS. Asher was at the end of the Land of Israel, as it is written with reference to his inheritance, and it reached to Carmel westward, and it is further stated, and its goings out were at the sea., Verse 29. And again it is said, Asher drove not out the inhabitants of Acco, which is located on the Great Sea [i.e., the Mediterranean], as the Rabbis have said: “At first [the ocean] advanced till Acco, and the second time till Japho.” And if so, Asher’s land was like the bars of the Land of Israel. Therefore, Moses said, Iron and brass shall be thy bars, that he will have [so to speak] doors of brass and iron bars, and the entire Land will be locked with them. This is an intimation that G-d will protect the whole Land from the enemy and the avenger. Or perhaps the verse states that strangers will not come to plunder the oil, for it will be transported from his land to the whole world in merchant ships.

ברזל ונחושת מנעלך וכימיך דבאך, may your door bolts be iron and copper, and your security last all your days.אין כאל ישורון, after Moses had completed his prayer concerning the tribes, he began blessing Israel as a whole.You, who are also known as Yeshurun, wear this title due to the nature of your power, אל, being different from all the other nations in two vital aspects. 1) other nations will not covet your land or try to invade it as they are afraid, something that proved true during the entire reign of Joshua and while any of the elders who were his advisers remained alive. (compare Joshua 24,31). Moses describes the land during that period as if bolted securely with heavy metal bolts, i.e. ברזל ונחושת מנעלך. 2) Your kingdom will not experience constant ups and downs such as the kingdoms of other nations whose position in the world constantly changes. כימיך דבאך, your position among the nations will be constant. The reason why I am certain that my blessing will materialise is that אין כא-ל רוכב שמים וארץ, no one else has a G’d that rides the heavens and the earth. Moses develops a theological/philosophical concept that contradicts that of the nations of the world, even those who recognise a supreme G’d who has created the universe. In their estimation, such a G’d would not bother to constantly stoop down to earth to see what goes on there, i.e. “ride both the heavens and the earth.” These nations believe that such matters must be left to delegates, such as the constellations of the stars, horoscopes, etc.

ברזל ונחושת, “iron and copper;” this is a metaphor for what are the sinews and bones for the body. They are for the body what the lock is on the door of the house.

וכימיך דבאך, “and as your days so shall be your strength.” Moses blesses Asher to be as agile and physically strong in old age as in its prime. The author quotes Rabbi Chanina saying in the Talmud, tractate Chulin, folio 24, that this Rabbi, at the age of 80, praised the Lord who had given him the strength to still tie his shoe laces while standing on one leg unsupported, (of course). He attributed this to how his mother, during his youth, had massaged oil into his bones and she had regularly bathed him in hot water.