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.

276. Verses 6b, 7, 8. And in the midst of the throne and around the throne were four animals, full of eyes before and behind. And the first animal was like a lion, and the second animal like a calf, and the third animal had a face like a man, and the fourth animal was like a flying eagle. And the four animals, each by itself had six wings round about, and they were full of eyes within, and they had no rest day and night, saying, Holy, holy, holy, Lord God Almighty, who was, and who is, and who is to come. "And in the midst of the throne and around the throne were four animals, full of eyes before and behind," signifies the Lord's guard and providence that the interior heavens be not approached except by the good of love and charity, that lower things depending thereon may be in order n. 277.

7. "And the first animal was like a lion," signifies the appearance, in ultimates of Divine truth proceeding from the Lord in respect to power and efficiency (n. 278; "and the second animal like a calf," signifies the appearance, in ultimates, of Divine good in respect to protection n. 279; "and the third animal had a face like a man," signifies the appearance, in ultimates, of the Divine guard and providence in respect to wisdom n. 280; "and the fourth animal was like a flying eagle," signifies the appearance, in ultimates, of the Divine guard and providence in respect to intelligence and as to circumspection on every side (n. 281-282.)

8. "And the four animals, each by itself, had six wings round about," signifies the appearance of the spiritual Divine on all sides about the celestial Divine n. 283; "and full of eyes within," signifies the Divine Providence and guard (n. 284); "and they had no rest day and night, saying, Holy, holy, holy," signifies that which is most holy proceeding from the Lord. n. 285); "Lord God Almighty, who was, and who is, and who is to come," signifies the infinite and eternal (n. 286).