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.

997. That the way of the kings from the rising of the sun might be prepared, signifies that the Divine truth from the Lord might flow in. This is evident from the signification of "the way of the kings," as being the influx of Divine truth, "way" signifying influx, and "kings" truths. The influx of Divine truth is meant because it is called "the way of the kings from the rising of the sun," for "ways" signify influx, since all influx from one society to another, thus from the Lord, is through ways opened in the spiritual world. And since "the rising of the sun" signifies where the Lord is, so "from the rising of the sun" means from the Lord. That the Lord is the sun of heaven, and therefore the "sun" means in the Word the Lord as to love, may be seen above (n. 401, 412, 527). (That "the east" and "the rising of the sun" mean where the Lord is, see n. 422; that "kings" signify Divine truths 29, 31, 553, 625.) What these words mean in the nearest sense has been told above, namely, that a way might be opened from the land of Canaan, which signifies the spiritual of the church, to Assyria, which signifies the rational of the church. The river Euphrates separated and bounded these countries. So "the way of the kings from the rising of the sun" signifies a passage from the church; and that this was opened is meant in that sense by "the water of the Euphrates was dried up."

[2] Something shall now be said about the influx into men of Divine truth from the Lord. From the Lord as a sun both heat and light proceed; but the heat is Divine good, and the light is Divine truth. The light, which is Divine truth, flows into and enters into every angel of heaven, and also into every man in the world, and gives internal sight, which is the sight of the understanding. For every man, not as to his body but as to his spirit, has a faculty for receiving that light, that is, for understanding the Divine truth. And that faculty is opened as the man grows up, and cultivates and forms his rational according to order, by the knowledges [scientifica] and by the cognitions [cognitiones] of good and truth. But the heat, which is Divine good, does not flow into an angel or a man as the light, which is Divine truth, does, for the reason that man is born into evils of every kind, and evils obstruct; consequently evils must first be removed before the heat, which is Divine good, can flow in; and evils are removed by looking upon them as sins against God and shunning them, by praying to the Lord for help; and so far as a man thus receives Divine good so far he comes into the light of understanding Divine truth. For the way of Divine truth into a man who is reformed is through the good of the will, and of the life therefrom with him.

[3] But when a man is not in Divine good, but in evil, he has nonetheless the faculty for receiving light, that is, for understanding Divine truth; and yet only so far as he is in a state separate from evil; if he is not in a state separate he has no such understanding of truth. A man is in a state separate when he is held solely in the thought that belongs to his understanding and not at the same time in the affection that belongs to his will. But in this state a man is not reformed, because the light does not then affect his life, that is, Divine truth is not then implanted. But man is in a state not separate when he is held in thought from the understanding and at the same time in affection from the will; and in that state man does not receive light, that is, does not understand Divine truth, unless he is at the same time in Divine good as to the affection of the will, for in that state the evils that belong to the will and the consequent falsities that belong to the thought obstruct and extinguish the light. But of these two states of man more will be said hereafter.

(Continuation respecting the Sixth Commandment)

[4] Since conjugial love in its first essence is love to the Lord from the Lord, and thus is innocence, conjugial love is also peace, such as the angels in the heavens have. For as innocence is the very being [esse] of all good, so peace is the very being [esse] of all delight from good, consequently is the very being [esse] of all joy between the marriage pair. As then, all joy is of love, and conjugial love is the fundamental love of all the loves of heaven, so peace itself has its seat chiefly in conjugial love. Peace is happiness of heart and soul arising from the conjunction of the Lord with heaven and the church, as well as from the conjunction of good and truth, when all conflict and combat of evil and falsity with good and truth has ceased, as may be seen above n. 365. And as conjugial love descends from such conjunction so all the delight of that love descends and derives its essence from heavenly peace. Moreover, this peace shines forth in the heavens as heavenly happiness from the faces of a marriage pair who are in that love, and who mutually regard each other from that love. But such heavenly happiness, which inmostly affects the delights of loves, and is called peace, can be granted only to those who can be joined together inmostly, that is, as to their very hearts.