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.

563. So the serpent spewed water out of its mouth like a river after the woman, that it might cause her to be swept away by the river. (12:15) This symbolizes a multitude of reasonings flowing from falsities in order to destroy the church.

The serpent symbolizes, here as above, the dragon leading astray. The woman symbolizes the New Church (no. 533). Water symbolizes truths, and in an opposite sense, falsities (no. 50, 409). A river symbolizes truths in abundance, and in an opposite sense, falsities in abundance (no. 409). Coming out of the mouth of the serpent symbolizes reasonings. So then, its spewing out water like a river symbolizes a multitude of reasonings flowing from falsities.

The reasonings of people meant by the dragon all arise from misconceptions and appearances, and if they are defended, they seem superficially to be true, but inwardly they contain a multitude of falsities.

I can relate this fact, that people in the church who affirm faith alone in themselves cannot afterward turn away from it without serious repentance, because they unite themselves with followers of the dragon who are currently in the world of spirits and in a state of agitation, being driven by their hatred for the New Church to harass all whom they encounter there. Moreover, because they unite with people on earth, as we said, they do not allow those who have once been captivated by their reasonings to withdraw from them; for they hold them as though bound in chains, and then shut their eyes so that they are no longer capable of seeing any truth clearly.