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 5
1
I saw, in the right hand of him who sat on the throne, a book written inside and outside, sealed shut with seven seals.
2
I saw a mighty angel proclaiming with a loud voice, "Who is worthy to open the book, and to break its seals?"
3
No one in heaven above, or on the earth, or under the earth, was able to open the book, or to look in it.
4
And I wept much, because no one was found worthy to open the book, or to look in it.
5
One of the elders said to me, "Don't weep. Behold, the Lion who is of the tribe of Judah, the Root of David, has overcome; he who opens the book and its seven seals."
6
I saw in the midst of the throne and of the four living creatures, and in the midst of the elders, a Lamb standing, as though it had been slain, having seven horns, and seven eyes, which are the seven Spirits of God, sent out into all the earth.
7
Then he came, and he took it out of the right hand of him who sat on the throne.
8
Now when he had taken the book, the four living creatures and the twenty-four elders fell down before the Lamb, each one having a harp, and golden bowls full of incense, which are the prayers of the saints.
9
They sang a new song, saying, "You are worthy to take the book, and to open its seals: for you were killed, and bought us for God with your blood, out of every tribe, language, people, and nation,
10
and made us kings and priests to our God, and we will reign on earth."
11
I saw, and I heard something like a voice of many angels around the throne, the living creatures, and the elders; and the number of them was ten thousands of ten thousands, and thousands of thousands;
12
saying with a loud voice, "Worthy is the Lamb who has been killed to receive the power, wealth, wisdom, strength, honor, glory, and blessing!"
13
I heard every created thing which is in heaven, on the earth, under the earth, on the sea, and everything in them, saying, "To him who sits on the throne, and to the Lamb be the blessing, the honor, the glory, and the dominion, forever and ever! Amen!"
14
The four living creatures said, "Amen!" The elders fell down and worshiped.
