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.

130. 1. No one is reformed by miracles and signs, because they compel. I have already explained [103, 119] that we have inner and outer processes of thought and that the Lord flows through our inner thought processes into the outer, this being the way he teaches and guides us. I have also explained [71-99] that it is the intent of the Lord's divine providence that we act in freedom and in accord with reason. Both of these abilities in us would be destroyed if miracles happened and we were forced into belief by them.

We can see the truth of this rationally as follows. We cannot deny that miracles induce faith and that they persuade us convincingly that what the miracle-worker says and teaches is true. To begin with, this conviction takes over the outer processes of our thought so completely that it virtually constrains and bewitches them. However, this deprives us of the two abilities called freedom and rationality and therefore of our ability to act in freedom and in accord with reason. Then the Lord cannot flow in through our inner thought processes into the outer ones; all he can do is leave us to convince ourselves by rational means of the truth of anything that has become a matter of faith for us because of the miracle.

[2] The basic state of our thought is that we look from our inner thinking and see things in our outer thinking in a kind of mirror, because as already noted [104] we can look at our own thinking, which can be done only by a deeper level of thinking. When we look at something in this mirrorlike way, we can turn it this way and that and shape it so that it seems attractive to us. If what we are looking at is something true, we could compare it to a good-looking, vibrant young woman or young man. However, if we cannot turn it this way and that and shape it but only believe it at second hand, influenced by a miracle, then even if it is true it is like a young woman or young man carved of stone or wood, with no life in it. We might also compare it to something that is constantly before our eyes, something that is all we look at, hiding whatever is on either side of it and behind it. Or we could compare it to a sound that is constantly in our ears, robbing us of any perception of the harmony of multiple sounds. This kind of blindness and deafness is imposed on our minds by miracles.

The same holds true for any conviction that is not looked at rationally before it becomes a conviction.