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.

3584. 'Cursed be those cursing you' means that the person who separates himself will be separated, while 'blessed be those blessing you' means that the person who joins himself will be joined. This is clear from the meaning of 'being cursed' as being separated from, and of 'being blessed' as being joined to, dealt with in 3504, 3514, 3530, 3565. These expressions have reference to truths - 'those cursing' meaning falsities, which sever themselves from truths, and 'those blessing' meaning truths, which link themselves to all other truths. For truths and goods are such that they form themselves into a community and at length constitute so to speak a single political unit. In the same way also such units group themselves together. The origins of all this lie in the form heaven takes. Within that form angels are positioned according to the blood relationships and relationships by marriage that exist between good and truth. In this way all the angels together constitute one kingdom or a single political unit. It is from this heavenly form that truths and goods flow in with man and become so positioned there that a similar form is produced, all of which is effected by the Lord alone. But what is involved here will be seen far more clearly from the correspondence of the Grand Man, which is heaven, with every single thing that exists with man. This correspondence will in the Lord's Divine mercy be dealt with at the ends of chapters. From these considerations it is now evident what Isaac's blessing, pronounced over Jacob but meant for Esau, embodies, namely the fruitfulness of good through the multiplication of truth, and of further fruitfulness of the latter.