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.

1250. That 'the mountain of the east' means charity, indeed charity from the Lord, is clear from the meaning of 'a mountain' in the Word as love to the Lord and charity towards the neighbour, as shown already in 795. And that 'the east' means the Lord, and consequently the celestial things of love and charity, see again what has appeared already in 101, and also in the following places: In Ezekiel,

The cherubs lifted up their wings. The glory of Jehovah went up from over the midst of the city and stood upon the mountain, which is on the east of the city. Ezekiel 11:22-23.

Here 'the mountain which is on the east' means nothing other than the celestial manifestation of the love and the charity that is the Lord's, for it is said that 'the glory of Jehovah stood there'. In the same prophet,

He brought me to the gate, to the gate facing the way of the east. And behold, the glory of the God of Israel came from the way of the east. Ezekiel 43:1-2.

Here 'the east' has a similar meaning.

[2] In the same prophet,

And he brought me back by the way of the outer gate of the sanctuary, which faces the east, and it was shut. And Jehovah said to me, This gate shall be shut and not opened, and no man shall enter by it; but Jehovah, the God of Israel, will enter by it. Ezekiel 44:1-2.

Here similarly 'the east' stands for the celestial manifestation of the love that is the Lord's alone. In the same prophet,

When the prince makes a freewill offering, a burnt offering, and peace offerings, as a freewill offering to Jehovah, one shall open for him the gate facing towards the east, and he shall make his burnt offering and his peace offerings, as he shall do on the sabbath day Ezekiel 46:12.

Here similarly it stands for that which is celestial, which essentially is love to the Lord.

[3] In the same prophet,

He brought me back to the door of the house, and behold, waters were issuing out from below the threshold of the house towards the east, for the house faced east. Ezekiel 47:1, 8.

This refers to the new Jerusalem 'The east' stands for the Lord, and so for the celestial manifestation of love, while 'waters' means things that are spiritual. Here the same is meant by 'the mountain of the east'. Furthermore those who dwelt in Syria were called 'the sons of the east', who will in the Lord's Divine mercy be spoken of later on.