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.

9419. 'And Moses rose up, and Joshua his minister' means the Word and its representative. This is clear from the representation of 'Moses' as the intermediary between the Lord and the people who are restricted to the outward sense of the Word, separated from the inward, thus also as the Word, as accords with what has already been shown just above in 9414; and from the representation of 'Joshua his minister' as its representative. The reason why 'Joshua' here means that representative is that what is representative serves and ministers, in order that the outward things of the Word and of worship may present themselves to the Lord through the intermediary, who was Moses. But these are matters such as are scarcely intelligible except to those who know about the ways in which a representation of the outward or literal sense of the Word is accomplished in heaven. That is to say, it is represented in one way with those who are acquainted with the outward sense of the Word and at the same time with the inward, that is, those who are acquainted with the outward sense of the Word and at the same time with true teachings of the Church, and in another way with those restricted to the outward sense, separated from the inward, as with this people. How it was accomplished with this people, see 4311.

[2] Some idea may be formed from this regarding the intermediary that 'Moses' represents and the ministering representative that 'Joshua' represents. That is to say, there is an inward holiness which Divine Truth emanating from the Lord possesses, thus which the Word and worship springing from it possess. This flows into heaven and is received there by angels. There is also an inflow of holiness indirectly through that inward holiness, as well as directly from the Lord, to good spirits present with a person engaged in reading the Word or in worship springing from it. This holiness is called an outward holiness, and when it flows in with a person it produces representative images formed in accord with the correspondences known to the person. All this helps one to see what use the intermediary serves, which Moses represents now, and what use the minister serves, which Joshua represents, namely that the outward holiness acts as intermediary, while the representative existing on the lowest level of order acts as minister. But it should be recognized that the idea of Divine Truth flowing in is unintelligible to a person unless the Lord sheds light on the idea. For the person sees what happens in no other way than this, that the holiness of the Word and the holiness of worship flows from the person to the Lord. But this order is inverted order, and is called physical influx, which is an appearance and not at all the reality; see what has been shown in the places referred to in 9223, 9227 (end).