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.

2268. 'Will You for five destroy the whole city?' means, Will mankind perish for the small amount that is lacking? This is clear from the meaning of 'five' as small, referred to immediately above, and from the meaning of 'a city' as truth, also dealt with already. The human mind as regards truths is in the Word compared to and also called 'a city', and as regards the goods that are present within truths is there compared to and also called 'the inhabitants'. For a similarity indeed exists, in that if the truths in a person's two memories ¹ and in the thoughts of his mind are devoid of goods, they are like a city that has no residents and so is vacant and empty. Indeed it can also be said of angels that they dwell so to speak in a person's truths and implant affections for good from the Lord when that person leads a life abiding in love to the Lord and in charity towards the neighbour, for they are delighted so to dwell, that is, to live, with such persons. It is different in the case of those with whom some truths exist but no goods that flow from charity.

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