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.

84. And behold I am alive unto the ages of the ages, signifies that eternal life is from Him. This is evident from the signification of "I am alive," which means to be from eternity, and that in Him alone is life from Himself (on which see above, n. 82); but here as being life in others, and His life in others is eternal life. For it is said just before that He "became dead," which signifies that He was rejected, because not received in faith and love; here, therefore, "I am alive" signifies that He is received by those who are in His life, which life is in faith and love with man, and that life is eternal life. That "unto the ages of the ages" signifies to eternity, is clear without explanation. That the life of the Lord is a life of faith in Him and love to Him, and that this life is eternal life is evident from many passages in the Word, as the following from John:

As Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up, that whosoever believeth in Him may not perish, but may have eternal life. He that believeth on the Son hath eternal life; but he that believeth not on the Son shall not see life (John 3:14-16, 36).

In the same:

The water that I shall give shall become in him a fountain of water, springing up unto eternal life (John 4:10-11, 14).

Water is the truth of faith (See above, n. 71).

In the same:

Everyone that beholdeth the Son, and believeth on Him, hath eternal life. The words that I speak unto you are spirit and are life (John 6:40, 63).

The "words" that the Lord speaks are also the truths of faith. In the same:

I am the resurrection and the life; he that believeth in Me, though he die, yet shall he live (John 11:25-26).

In the same:

Work for the food which abideth unto eternal life, which the Son of man giveth (John 6:27).

The "food" which the Lord gives is also the truth and good of faith, because spiritual food is meant (See Arcana Coelestia 3114, 4459, 4792, 5147, 5293, 5340, 5342, 5410, 5426, 8562, 9003). It was said that the life of the Lord is in faith in Him and love to Him with man; this is because everything of faith and love is from Him, and that which is from Him is also Himself, for it is His proceeding Divine, which is called "the Spirit of Truth" and "the Holy Spirit;" and as the Lord is therein, and it is Himself, therefore it is said that they should abide in the Lord, which means in faith in Him and love to Him, from Him; as in John:

Jesus said, Abide in Me, and I in you. If ye abide in Me, and My words abide in you, ye shall ask whatever ye will, and it shall be done unto you. Abide in My love. If ye keep My commandments, ye shall abide in My love. He that abideth in Me, and I in him, the same beareth much fruit; for without Me ye cannot do anything (John 15:4-10).

From this it may be known what is meant by these words in John:

Ye see Me; because I live ye shall live also (John 14:19).

(That to "see" the Lord is to believe in Him, see above, n. 14, 25, 37; and that "to have faith," or "to believe" in the Lord, is to be in love and charity, see the little work on The Last Judgment 33-39; and New Jerusalem and Its Heavenly Doctrine, n. 108-142.)