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.

7077. Because spirits belonging to Mercury are like this and yet possess such an abundance of knowledge they are full of a particular kind of pride, 6813, which leads them to suppose that they possess so much that there can be scarcely any more for them to know. But they have been told by spirits from our planet that they know not much but little, and that the amount they do not know is in comparison infinite. What they do not know, they are told, compared with what they do know is like the waters of a vast ocean compared with the water of a tiny spring. To enable them to know that this was so, some angelic spirit was allowed to talk to them and to tell them in general terms what it was they knew and what it was they did not know, and to tell them that the number of the things they did not know was infinite and that eternity would be too short to allow them to have even a general knowledge of things. That spirit used the language of heavenly ideas to speak to them. He did so far more readily than they; and because he revealed to them what it was they knew and did not know they were struck with amazement. After that I saw another angel talking to them; he appeared rather high up over to the right. He listed very many things they did not know, and then went on to talk to them by means of changes of state, which they said they did not understand. At that point he told them that each change of state, and also each smallest part of it, contained infinite aspects. Because they were filled with pride on account of the items of knowledge in their possession they began, when they heard this, to humble themselves. Their humility was represented by a sinking downwards of the scroll which they formed (for that group appeared at that time as a scroll, in a forward position over on the left, at a distance, on the level of the region beneath the navel). But the scroll looked as though it had caved in in the middle and was raised up at the ends. A movement to and fro in it was also noticeable. They were also told what this scroll was a sign of, namely what they thought in their state of humility, and that those who were seen at the raised ends did not as yet have any humility. I then saw a separation take place in the scroll, and those without humility were banished to their own world while the rest remained behind. Because spirits from the planet Mercury, who flee from spirits belonging to ours on account of their interest in material things, asked whether such could become angels, 6929, they now received the reply that the angel who spoke to them came from our planet.