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.

8898. 'In order that your days may be prolonged on the land' means the resulting state of life in heaven. This is clear from the meaning of 'being prolonged' as that which has reference to good and the increase of it, dealt with below; from the meaning of 'your days' as states of life, dealt with in 23, 487, 488, 493, 893, 2788, 3462, 3785, 4850, 5672, 5962, 6110, 7680, 8426; and from the meaning of 'the land' - at this point the land of Canaan, since the children of Israel are told 'it is the land which Jehovah your God gives you' - as the Lord's kingdom, dealt with in 1413, 1437, 1607, 1866, 3038, 3481, 3686, 3705, 4240, 4447. The reason why 'being prolonged' has reference to good and the increase of it is that the prolongation of days is the length of time that life will last, and in heaven there is neither time nor space, but states instead of them. Therefore 'being prolonged', since it has reference to a state in respect of good, means the increase of it. For length is spoken of in regard to good, and breadth to truth, see 1613, 4482; and in heaven there are no areas of space, just as there are no periods of time, but states instead of them, 1274, 1382, 2625, 2788, 2837, 3254, 3356, 3404, 3938, 4321, 4814, 4882, 4901, 4918, 5605, 6110, 7218, 7381.