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.
Matthew 23:29-37
29
"Woe to you, scribes and Pharisees, hypocrites! For you build the tombs of the prophets, and decorate the tombs of the righteous,
30
and say, 'If we had lived in the days of our fathers, we wouldn't have been partakers with them in the blood of the prophets.'
31
Therefore you testify to yourselves that you are children of those who killed the prophets.
32
Fill up, then, the measure of your fathers.
33
You serpents, you offspring of vipers, how will you escape the judgment of Gehenna?
34
Therefore, behold, I send to you prophets, wise men, and scribes. Some of them you will kill and crucify; and some of them you will scourge in your synagogues, and persecute from city to city;
35
that on you may come all the righteous blood shed on the earth, from the blood of righteous Abel to the blood of Zachariah son of Barachiah, whom you killed between the sanctuary and the altar.
36
Most certainly I tell you, all these things will come upon this generation.
37
"Jerusalem, Jerusalem, who kills the prophets, and stones those who are sent to her! How often I would have gathered your children together, even as a hen gathers her chicks under her wings, and you would not!
