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.

6068. 'And behold, they are in the land of Goshen' means that they are in the middle of the natural where factual knowledge resides. This is clear from the meaning of 'Goshen' as the middle or inmost part of the natural, dealt with in 5910, 6028, 6031. What is meant by their being in the middle of the natural is this: Once the Church's forms of good and its truths - that is, those which it has received from the Lord's Word - have been acknowledged and with faith accepted in the natural, they occupy the middle there. For things that are immediate objects of attention are in the middle, and those that are not immediate objects of attention are to the sides; consequently the ones in the middle are seen clearly, those to the sides vaguely.

[2] It is the same as it is with the sight of the eye. The objects on which the eye is directly focused are in the middle, that is, in the centre and are seen clearly; but those on which it is not directly focused are to the sides, away from the middle, and are seen vaguely. For the inner eye, which is the intellectual power of the mind and which depends for its vision on the light of heaven, sees things outside itself in the natural, which are known facts, just as the physical eye sees objects or a whole range of objects outside itself. Inward sight is directed towards the things that give the greatest delight and are close to the heart, and it fixes its attention directly on them, in the same way as outward sight focuses on things similarly delightful in whole ranges of objects. Inward sight accordingly focuses on those known facts that are in close agreement with the truth and good that govern a person. These facts are then, for that person, in the middle. The reason why inward sight sees factual knowledge is that such sight is spiritual and therefore directs its attention towards spiritual matters, thus towards known facts, for these are the appropriate objects of spiritual attention.