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.

2088. 'Behold I will bless him, I will make him fruitful, and I will multiply him, more and more' means that they were to be furnished and endowed with goods of faith and with truths from that source, without limit. This is clear from the meaning of 'being blessed', 'being fruitful', and 'being multiplied'. 'Being blessed' means being endowed with all goods, as shown in Volume One, in 981, 1096, 1420, 1422. 'Being fruitful' means the goods of faith with which they were to be endowed, and 'being multiplied' the truths from that source, as also shown in Volume One, in 43, 55, 913, 983.

[2] Who exactly are celestial people and who spiritual would take too long to describe here. See where they have been described already, for example in 81, 597, 607, 765, 2069, 2078, and many times elsewhere. In general celestial people are those who have love to the Lord, and spiritual those who have charity towards the neighbour. For the distinction between having love to the Lord and having charity towards the neighbour, see above 2023. Celestial people are those whose affection for good stems from good, but spiritual people are those whose affection for good stems from truth. To begin with all people were celestial, because they were governed by love to the Lord, and from this they received perception by which they perceived what was good, not from truth but from the affection for good.

[3] But after this, when love to the Lord was no longer what it had been, spiritual people took their place, these being called spiritual when they were governed by love towards the neighbour, which is charity. But love towards the neighbour, or charity, was implanted by means of truth and in this way they received a conscience in accordance with which they acted, not from an affection for good but from an affection for truth. With them charity looks like the affection for good, but is in fact the affection for truth. Because it looks like the affection for good charity is still referred to as good. But that good is a good arising out of their faith. It is these who are meant by the Lord in John,

I am the door. If anyone enters by Me he will be saved, and will go in and out, and find pasture. I am the good Shepherd; and I know My own and am known by My own. And other sheep I have which are not of this fold; I must bring them also, and they will hear My voice, and there will be one flock and one Shepherd. John 10:9, 14, 16.