Altar
The first altar mentioned in the Word was the one built by Noah after he came out of the ark, after being saved from the great flood. On that altar, he sacrificed clean animals to the Lord.
Mountains represent the Lord because of their height; we need to raise our thoughts above worldly things when "talking" with the Lord. An altar is a small artificial mountain. When it's used in worship, it can call to mind this raising of thought. The fire and smoke that rise from an altar are symbolically being sent to the Lord.
Most altars were made from unhewn stones. Stones represent truths. Unhewn stones - ones that have not been shaped by men - represent truths from the Word, truths that have not been adulterated.
The clean beasts to be sacrificed represent good things, charitable acts done because they are right. The clean birds represent thoughts about doctrine and actions, and about what is right. Presenting these things is an acknowledgment that we have them from the Lord, and a giving thanks to Him for them.
In the Israelitish Tabernacle, the altar of burnt offering represented the acknowledgment of good and the altar of incense that of truth. For this reason this larger altar, which was outside by the door, was made of brass which signifies natural good, while the altar of incense was made of gold, which signifies love to the Lord from whom comes truth.
Jeremiah 13:1-12
1
Thus says Yahweh to me, Go, and buy yourself a linen belt, and put it on your waist, and don't put it in water.
2
So I bought a belt according to the word of Yahweh, and put it on my waist.
3
The word of Yahweh came to me the second time, saying,
4
Take the belt that you have bought, which is on your waist, and arise, go to the Euphrates, and hide it there in a cleft of the rock.
5
So I went, and hid it by the Euphrates, as Yahweh commanded me.
6
It happened after many days, that Yahweh said to me, Arise, go to the Euphrates, and take the belt from there, which I commanded you to hide there.
7
Then I went to the Euphrates, and dug, and took the belt from the place where I had hidden it; and behold, the belt was marred, it was profitable for nothing.
8
Then the word of Yahweh came to me, saying,
9
Thus says Yahweh, In this way I will mar the pride of Judah, and the great pride of Jerusalem.
10
This evil people, who refuse to hear my words, who walk in the stubbornness of their heart, and are gone after other gods to serve them, and to worship them, shall even be as this belt, which is profitable for nothing.
11
For as the belt clings to the waist of a man, so have I caused to cling to me the whole house of Israel and the whole house of Judah, says Yahweh; that they may be to me for a people, and for a name, and for a praise, and for a glory: but they would not hear.
12
Therefore you shall speak to them this word: Thus says Yahweh, the God of Israel, Every bottle shall be filled with wine: and they shall tell you, Do we not certainly know that every bottle shall be filled with wine?
