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.

3138. These three verses deal with the preparation and enlightenment of the natural man so that the truth which was to be joined to good in the Rational might be summoned from there. With regard to that preparation and enlightenment the position is that there are two kinds of light which shape man's intellectual concepts - the light of heaven, and the light of the world. The light of heaven comes from the Lord who to angels in the next life is the Sun and Moon, see 1053, 1521, 1529, 1530. The light of the world comes from the sun and moon which a person sees with his physical eyes. The internal man receives his sight and understanding from the light of heaven whereas the external man receives his sight and understanding from the light of the world. The influx of the light of heaven into ideas formed in the light of the world produces enlightenment and at the same time recognition - the recognition of truth if a correspondence exists, the recognition of falsity instead of truth if that correspondence does not exist. But enlightenment and recognition are not possible unless affection or love is present, which is spiritual warmth and imparts life to the things illumined by the light. This may be compared to the light of the sun. It is not the light of the sun but the warmth within the light that imparts life to plants, as is evident from the seasons of the year.

[2] The verses which follow immediately after this describe the preparation further - the light of heaven, which is the Lord's Divine light, flowed into the ideas formed in the light of the world in His natural man so that He might bring forth from there the truth that was to be joined to good in the Rational. Thus it was to be brought forth in what is the ordinary way. Therefore to make His Human Divine the Lord came into the world in the ordinary way, that is, He was willing to be born as any other person is born, to receive instruction as any other does, and to be born again as any other, but with this difference: Man is born again from the Lord, whereas the Lord not only regenerated Himself from Himself, but also glorified Himself, that is, made Himself Divine; also man is made new through the influx of charity and faith, whereas the Lord was made so through the influx of Divine Love that was within Him and that was His own. From this it may be seen that man's regeneration is an image of the Lord's glorification, or what amounts to the same, that in the process of man's regeneration as the image one can envisage, though remotely, the process of the Lord's glorification.