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.
Revelation 8
1
When he opened the seventh seal, there was silence in heaven for about half an hour.
2
I saw the seven angels who stand before God, and seven trumpets were given to them.
3
Another angel came and stood over the altar, having a golden censer. Much incense was given to him, that he should add it to the prayers of all the saints on the golden altar which was before the throne.
4
The smoke of the incense, with the prayers of the saints, went up before God out of the angel's hand.
5
The angel took the censer, and he filled it with the fire of the altar, and threw it on the earth. There followed thunders, sounds, lightnings, and an earthquake.
6
The seven angels who had the seven trumpets prepared themselves to sound.
7
The first sounded, and there followed hail and fire, mixed with blood, and they were thrown to the earth. One third of the earth was burnt up, and one third of the trees were burnt up, and all green grass was burnt up.
8
The second angel sounded, and something like a great burning mountain was thrown into the sea. One third of the sea became blood,
9
and one third of the living creatures which were in the sea died. One third of the ships were destroyed.
10
The third angel sounded, and a great star fell from the sky, burning like a torch, and it fell on one third of the rivers, and on the springs of the waters.
11
The name of the star is called "Wormwood." One third of the waters became wormwood. Many people died from the waters, because they were made bitter.
12
The fourth angel sounded, and one third of the sun was struck, and one third of the moon, and one third of the stars; so that one third of them would be darkened, and the day wouldn't shine for one third of it, and the night in the same way.
13
I saw, and I heard an eagle, flying in mid heaven, saying with a loud voice, "Woe! Woe! Woe for those who dwell on the earth, because of the other voices of the trumpets of the three angels, who are yet to sound!"
