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.

2130. As regards the second representation, that is to say, the idea of a Last Judgement which takes place before the eyes of the good when they are being admitted into heaven, let that too be described. In the Word it is said that the door was shut, so that they could no longer be admitted; and that they had no oil, arrived too late, and therefore were not admitted, statements which also mean a Last-Judgement state. The situation with these matters and how they are to be understood has been shown to me.

[2] I heard communities of spirits declaring in a clear voice, one community after another, that a wolf had wished to carry them off but that the Lord rescued them, and so they were restored to Him, and on that account rejoiced from the depths of their heart. Indeed they had been without hope, and so were afraid that the door had been shut, and that they had arrived too late to be admitted. Such thought had been instilled into them by those called wolves, but it vanished on their being admitted, that is, being received, by angelic communities. Being admitted into heaven is nothing else. The admission which I witnessed seemed to proceed continuously community by community, up to twelve of them, the admission, that is, the reception, of the twelfth being more difficult than that of the previous eleven. After that about eight more communities were also admitted, which, it was pointed out to me, were composed of females. Having witnessed all this I was told that this is how the process of admission, that is, of being received into heavenly communities is seen. They proceed in an orderly continuation from one place to another. I was also told that heaven can never be filled up, still less the door be shut, but that the more who enter, the more blessing and happiness there is for those in heaven, because their unanimity is made that much stronger.

[3] After these had been admitted it did at that point seem as though heaven was shut; for there were still more who wished after that to be admitted, that is, to be received. But they were told in reply that they could not yet be let in. This is meant by those arriving too late, by the door being shut, by their knocking, and by the statement about their having no oil in their lamps. The reason they were not admitted was that they were not yet ready to move among angelic communities where mutual love exists, for, as stated above towards the end of 2119, people who in the world have lived charitably disposed towards the neighbour are raised up by the Lord into heaven gradually.

[4] There were also other spirits who did not know what heaven is, namely mutual love, and who also at that time wished to be admitted. They imagined it was just a matter of being admitted. They received the reply however that it was not yet time for them, but that they would be admitted at another time when they were ready for it. The reason why twelve communities were seen was that 'twelve' means everything comprising faith, as stated above towards the end of 2129.