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.
Numbers 23:1-7
1
Balaam said to Balak, "Build me here seven altars, and prepare me here seven bulls and seven rams."
2
Balak did as Balaam had spoken; and Balak and Balaam offered on every altar a bull and a ram.
3
Balaam said to Balak, "Stand by your burnt offering, and I will go: perhaps Yahweh will come to meet me; and whatever he shows me I will tell you." He went to a bare height.
4
God met Balaam: and he said to him, "I have prepared the seven altars, and I have offered up a bull and a ram on every altar."
5
Yahweh put a word in Balaam's mouth, and said, "Return to Balak, and thus you shall speak."
6
He returned to him, and behold, he was standing by his burnt offering, he, and all the princes of Moab.
7
He took up his parable, and said, "From Aram has Balak brought me, the king of Moab from the mountains of the East. Come, curse Jacob for me. Come, defy Israel.
