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.

1209. Verse 5. And a voice came forth from the throne signifies the unanimity of the whole heaven. This is evident from the signification of "a voice coming forth from the throne," as being the unanimity of the whole heaven, namely, in glorifying the Lord; for "throne" signifies the whole heaven because the Lord is on it, and the Lord is heaven itself. The angels of whom heaven consists do not make anything of heaven from what is of their own; but it is the Divine with them that proceeds from the Lord that makes heaven; and this is why "a voice out of heaven" signifies the unanimity of all the heavens, or of the whole heaven. (That a "throne," when the Lord is treated of, signifies heaven, may be seen n. 253, 462, 477)

(Continuation)

[2] 4. In everything spiritual there are three forces, an active force, a creative force, and a formative force. The active force, because it is spiritual, proceeds from the fountain of all forces, which is the sun of heaven, and that is the Lord's Divine love, and love is the active itself, from which the living force which is life proceeds.

[3] The creative force is the force that produces causes and effects from beginning to end, and reaches from the First through intermediates to the last. The First is the sun of heaven itself, which is the Lord; intermediates are things spiritual, afterwards things natural, also things terrestrial, from which finally are productions. And as in the creation of the universe that force proceeded from the First to the last, so afterwards it proceeds in like manner in order that productions may be continual; otherwise they would fail. For the First continually regards the last as an end; and unless the First looked to the last continually from itself through intermediates according to the order of creation, all things would perish; therefore productions, which are especially animals and plants, are continuations of creation. It does not matter that the continuations are effected by seeds, it is still the same creative force that produces. Moreover, it is according to the observation of some that certain seeds are yet being produced.

[4] The formative force is the last force from ultimates, for it is the force that produces animals and plants from the ultimate materials of nature, which are collected in the earth. The forces that are in nature from its origin, which is the sun of the world, are not living forces but dead forces. These do not differ from the forces of heat in man and animal, which keep the body in such a state that the will by means of affection, and the understanding by means of thought, which are spiritual, can flow in and do their work in it. They do not differ from the forces of light in the eye, which simply cause the mind, which is spiritual, to see by means of its organ, the eye. The light of the world sees nothing, but the mind by the light of heaven. The same is true of plants. He that believes that the heat and light of the sun of the world do anything more than open and dispose the things proper to nature that they may receive influx from the spiritual world is very much deceived.