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.

1155. 'The sons of Javan' means others again with whom there existed external worship derived from the worship existing with the nation Javan. This in like manner becomes clear in the Prophets where they are named in connection with real things and mean nothing other than those things. The reason the sons of Gomer and the sons of Javan are named, but not the rest of the seven mentioned in verse 2, is that the sons of the one have reference to the branch of spiritual things, and the sons of the other to the branch of celestial things. The fact that 'the sons of Gomer' has reference to the branch of spiritual things is clear from the places in the Prophets quoted just above, while the fact that 'the sons of Javan' has reference to the branch of celestial things will be evident from what follows. The branch of spiritual things differs from that of celestial through this - that spiritual have regard to truths of faith but celestial to the goods of faith which are the expressions of charity. Although the world is totally ignorant of these differences they are nevertheless very well known in heaven, not only indeed as regards general but also as regards specific differences. In heaven not the smallest difference exists which is not distinct and separate within a perfect ordering. The world knows only of the existence of forms of worship, and the fact that these vary from one another. And even then it knows only of differences in externals. In heaven however the very differences themselves which are countless are plain to see, and indeed the internal nature of them.