Brass and iron as in Isaiah 48:4 and Daniel 7:19 signify what is hard.

In Genesis 4:22, brass signifies natural good. (Arcana Coelestia 421)

In Numbers 21:9, this signifies the Lord's divine natural. (Apocalypse Revealed 49)

Brass also signifies the good in man's natural and the sensuous in the Lord. (Arcana Coelestia 197, Apocalypse Revealed 49, Apocalypse Explained 705)

(Odkazy: Apocalypse Explained 70)

70. The feet are said to be "like unto burnished brass," because burnished brass is polished brass, shining from something fiery; and "brass" in the Word signifies natural good. Metals are equally significative with the rest in the Word. "Gold" in the Word signifies celestial good, which is inmost good; "silver" signifies the truth thereof, which is spiritual good: "brass" natural good which is outmost good, and "iron" the truth thereof, which is natural truth.

Metals have such significations from correspondence; for in heaven many things are seen shining as if from gold and silver, and also many things as if from brass and iron; and it is there known that by these the goods and truths mentioned above are signified. It was from this that the ancients, who had a knowledge of correspondences, named the ages according to these metals; calling the first age the "golden," because innocence, love, and wisdom therefrom then ruled; but the second "silver," because truth from that good, or spiritual good, and intelligence therefrom then ruled; the third age "brazen" or "copper," because mere natural good, which is justness and sincerity of moral life, then ruled; but the last age they called "iron," because mere truth without good then ruled, and when that rules, falsity also rules. All this was from the spiritual signification of these metals.

[2] From this it can be known what is signified by the image seen in a dream by Nebuchadnezzar:

The head of which was of gold, the breast and arms of silver, the belly and sides of brass, the legs of iron, and the feet partly of iron and partly of clay (Daniel 2:23, 33);

namely, the state of the church in respect to good and truth, from its first time to its last; its last time was when the Lord came into the world. When it is known that "gold" signifies celestial good, "silver" spiritual good, "brass" natural good, and "iron" natural truth, many arcana in the Word, where these metals are mentioned, can be understood. Thus what is signified by these words in Isaiah:

For brass I will bring gold, for iron I will bring silver, and for wood brass, and for stones iron; I will also make thy government peace, and thine exactors justice (Isaiah 60:17).

[3] But as the signification of "brass," as meaning natural good, is here treated of, I will cite only a few passages where "brass" is mentioned, as signifying that good. Thus in Moses:

Asher acceptable unto his brethren, and dipping his foot in oil. Thy shoe iron and brass, and as thy days thy fame (Deuteronomy 33:24-25).

"Asher," as one of the tribes, signifies the blessedness of life, and the delight of affections (See Arcana Coelestia 3938-3939, 6408); "to dip the foot in oil" signifies natural delight, "oil" is delight (See n. 9954), "foot" the natural (See just above, n. 69; "the shoe iron and brass" signifies the lowest natural from truth and good, "the shoe" is the lowest natural (See n. 1748, 1860, 6844), "iron" is its truth, and "brass" its good (as above). In the same:

Jehovah thy God will bring thee into a wealthy land; a land out of whose stones thou mayest hew out iron, and out of its mountains brass (Deuteronomy 8:7, 9).

In Jeremiah:

I will give thee unto this people for a fortified wall of brass, that they may fight against thee and not prevail against thee (Jeremiah 15:20).

And in Ezekiel:

Javan, Tubal, and Meshech, they were thy traffickers; with the soul of man and with vessels of brass they traded thy merchandise (Ezekiel 27:13).

In this chapter the traffickings of Tyre are treated of, by which are signified the knowledges of good and truth; by the names "Javan," "Tubal," and "Meshech," are signified such things as are of good and truth, of which knowledges treat; the "soul of man" is truth of life; "vessels of brass" are scientifics of natural good. (What is signified by "Tyre" may be seen in Arcana Coelestia 1201; what by "traffickings," n. 2967, 4453; what by "Tubal and Meshech," n. 1151; what by "Javan," n. 1152, 1153, 1155; what by the "soul of man," n. 2930, 9050, 9281; what by "vessels," n. 3068, 3079, 3316, 3318) In the same:

The feet of the cherubs sparkled like the appearance of polished brass (Ezekiel 1:7).

What "cherubs" and "feet" signify, see above n. 69.

[4] In the same:

I saw and behold there was a man, whose appearance was like the appearance of brass, and a line of flax was in his hand; and he was standing in the gate (Ezekiel 40:3).

It was because this angel measured the wall and the gates of the house of God, which signify the externals of the church, that his appearance was seen as the appearance of brass. He who knows that "brass" signifies the external of the church, which in itself is natural, can in some measure know why:

The altar of burnt-offering was overlaid with brass, and the grating about it was of brass, and the vessels of brass (Exodus 27:1-4);

as also why:

The great vessel, which was called the sea, with the twelve oxen under it, and the ten lavers with the bases, and also all the vessels of the tabernacle for the house of God, were made by Solomon of polished brass (1 Kings 7:43-47).

[5] He who knows what "brass" signifies may also enter into the arcanum why it was commanded that a serpent of brass be set up for the people to look at, of which it is thus written in Moses:

Jehovah sent serpents among the people, and they bit the people. And He said unto Moses, Make thee a serpent, and set it upon a standard, and it shall come to pass that everyone that is bitten, and looketh upon it, shall live. And Moses made a serpent of brass, and set it upon a standard; and it came to pass, that if a serpent had bitten any man, and he looked unto the serpent of brass, he lived (Numbers 21:6, 8-9).

That this "serpent" signified the Lord, He Himself teaches in John:

As Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up, that whosoever believeth in Him may not perish, but may have everlasting life (John 3:14-15).

By the "serpent" is signified that which is the ultimate of life with man, and is called the external sensual, which is the natural. Because this ultimate in the Lord was Divine, a serpent of brass was made among the sons of Israel, with whom all things were representative; and this signified that if they would look to the Divine Human of the Lord they would live again, that is, if they would believe in Him they would have eternal life, as the Lord Himself also teaches. (That to "see" is in the spiritual sense to believe, see above, n. 37, 68; and that the "serpent" is the external sensual, which is the ultimate of man's life, see Arcana Coelestia 195-197, 6398, 6949, 10313) That "brass" and "iron" in the Word also signify what is hard (as in Isaiah 48:4; Daniel 7:19 where), will be seen in what follows.