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.
Isaiah 31:1-3
1
Woe to those who go down to Egypt for help, and rely on horses, and trust in chariots because they are many, and in horsemen because they are very strong, but they don't look to the Holy One of Israel, and they don't seek Yahweh!
2
Yet he also is wise, and will bring disaster, and will not call back his words, but will arise against the house of the evildoers, and against the help of those who work iniquity.
3
Now the Egyptians are men, and not God; and their horses flesh, and not spirit. When Yahweh stretches out his hand, both he who helps shall stumble, and he who is helped shall fall, and they all shall be consumed together.
