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.

1990. 'Jehovah appeared to Abram' means manifestation. This is clear without explanation, for, as has been stated, Abram represents the Lord. No human being at all in the whole world has seen Jehovah, the Lord's Father; the Lord alone has done that, as He Himself has stated in John,

Nobody has ever seen God; the only begotten Son who is in the bosom of the Father, He has made Him known. John 1:18.

In the same gospel,

You have never heard His voice nor seen His shape. John 1:37.

And again in the same gospel,

No one has seen the Father except Him who is with the Father, He has seen the Father. John 6:46.

[2] The Infinite itself which stands above all the heavens and above man's inmost being cannot be manifested except by means of the Divine Human, which exists solely with the Lord. Communication of the Infinite with finite beings is not possible at all from any other source. This also explains why, when Jehovah appeared to members of the Most Ancient Church and subsequently to members of the Ancient Church which existed after the Flood, and also after that to Abraham and the prophets, He was manifested to them as a human being. That it was indeed the Lord, He Himself openly teaches in John,

Abraham your father rejoiced to see My day, and saw it and was glad. Truly, truly, I say to you, Before Abraham was, I am. John 8:56, 58.

This is also taught in the Prophets, for example in Daniel who saw Him as 'a son of man', Daniel 7:13.

[3] From these quotations it becomes clear that the Infinite Being (Esse), which is Jehovah, could not possibly be manifested to man except through the Human Essence, that is, through the Lord, and so has not been manifested to anyone except the Lord alone. So that He could be present with and be joined to mankind, after mankind had removed itself entirely from the Divine and had immersed itself in foul desires and so in merely bodily and earthly things, He adopted the Human Essence itself by being born. He did so in order that the Infinite Divine could be joined to man even though man was so remote. Otherwise mankind would have died the death of those for ever damned. As for all the other arcana concerning the manifestation of Jehovah in the Lord's Human, when His state was a state of humiliation, before He had fully united the Human Essence to the Divine Essence and glorified it, these will in the Lord's Divine mercy be explained later on, to the extent that they are capable of being understood.