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.

2807. 'Abraham said, God will see for Himself to the animal for a burnt offering, my son' means the reply: The Divine Human will provide those who are to be sanctified. This is clear from the meaning of 'seeing to for oneself', when used in reference to God, as foreseeing and providing - for 'to see' in the internal sense nearest to the literal means to understand, 2150, 2325, whereas in the sense yet more interior it means having faith, 897, 2325, while in the highest sense it means foreseeing and providing; and also from the meaning of 'the animal for a burnt offering' as those members of the human race who are to be sanctified, dealt with just above in 2805. That 'the animal for a burnt offering' is here used to mean those who are spiritual is evident from what follows. The kinds of animals used for burnt offering and sacrifice each had a different meaning. That is to say, a lamb meant one thing, a sheep another, a kid and she-goat another, a ram and he-goat another, an ox yet another, as did a young bull and a calf. And young pigeons and turtle doves had meanings different again. It is quite clear that each kind of animal had its own meaning from the fact that it was laid down explicitly which kind were to be sacrificed on each particular day, at each particular religious festival, when atonement was being made, cleansing effected, inauguration carried out, and all other occasions. Which kinds were to be used on which occasions would never have been laid down so explicitly unless each one had possessed some specific meaning.

[2] Clearly all the religious observances or forms of external worship which existed in the Ancient Church, and subsequently in the Jewish, represented the Lord, so that the burnt offerings and sacrifices in particular represented Him since these were the chief forms of worship among the Hebrew nation. And because they represented the Lord they also at the same time represented among men those things that are the Lord's, that is to say, the celestial things of love, and the spiritual things of faith, and as a consequence of this represented the people themselves who were celestial and spiritual or who ought to have been so. This is why 'the animal' here means those who are spiritual, that is, those who belong to the Lord's spiritual Church. As regards 'God will see for Himself to the animal for a burnt offering, my son' meaning that the Divine Human will provide them, this is clear from the fact that here it is not said that 'Jehovah' will see to it but that 'God' will do so. When both of these names occur, as they do in this chapter, Jehovah is used to mean the same as 'the Father', and God the same as 'the Son', so that here the Divine Human is meant; and a further reason for the usage is that the spiritual man, whose salvation comes from the Divine Human, is the subject, see 2661, 2716.