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.

4156. 'And put them in the camel's straw' means in facts. This is clear from the meaning of 'the camel's straw' as facts, 3114. These are called straw not only because straw is the food for camels but also because facts, compared with rational ideas, are coarse and lacking in order. For the same reason too facts are meant by 'the entangled boughs of trees and of the wood', 2831. Also 'camels' means general facts that belong to the natural man, see 3048, 3071, 3143, 3145.

[2] As to the assertion that facts, compared with rational ideas, are coarse and lacking in order and for that reason are meant by 'straw' and also by 'entangled boughs', as has been stated, this idea is not open to those who rely solely on facts and are on that account reputed to be learned. They believe that the amount a person knows, that is, how much knowledge he possesses, determines how wise he is. But the situation is quite different, as has been made clear to me from those in the next life who, when they lived in the world, relied solely on facts and as a result acquired a name and reputation for being learned. Such people are sometimes far more stupid than those who have not possessed any skill in the use of factual knowledge. The reason for that stupidity has also been disclosed to me, which is this: Facts are indeed a means towards becoming wise, but they can also be a means towards becoming insane. For people who are leading a good life facts are a means to becoming wise, but for those leading an evil life they are a means to becoming insane since they use facts to support not only a life of evil but also false assumptions, which they do arrogantly and convincingly because they believe that they are wiser than others.

[3] This leads to the destruction of their rational. It is not the person who is able to reason from facts, doing so sometimes in a seemingly more masterly way than others, who is endowed with rationality. This skill which he possesses is the product of a wholly illusory light. But that person has the proper gift of rationality who is able to see clearly that good is good and truth is truth, and as a consequence that evil is evil and falsity is falsity. But anyone who looks on good as evil and on evil as good, and who also looks on truth as falsity and falsity as truth, cannot in any sense be called rational, but rather irrational, no matter how capable he is at reasoning. With the person who sees clearly that good is good and that truth is truth, and conversely that evil is evil and falsity is falsity, there is light flowing in from heaven and enlightening the area of his understanding and causing reasons which he sees with the understanding to be just so many rays of that light. The same light also gives light to facts so that they serve to support those reasons, besides imposing order and the heavenly form on such facts. People however who stand opposed to good and truth, as all do who are leading an evil life, do not allow that heavenly light in. Instead they take delight solely in their own illusory light, whose nature is such that one sees things rather like a person in the dark who sees streaks on a wall, and is deluded into making all kinds of shapes out of them, when yet they are not shapes, for as daylight falls on them they are seen to be merely streaks.

[4] From all this it may be seen that facts are a means to becoming wise and also a means to becoming insane; that is, that they are a means to perfecting the rational or else a means to destroying it. Those therefore who have destroyed the rational by means of facts are in the next life far more stupid than those who have not possessed any skill in the use of factual knowledge. The coarseness of facts compared with rational ideas is evident from the consideration that they belong to the natural or external man, and that the rational which is cultivated by means of them belongs to the spiritual or internal man. How far facts are different from and distant from the rational as regards purity can be known from what has been stated and shown about the two memories in 2469-2494.