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.

5265. 'The seven good cows are seven years' means a state when truth within the interior natural is multiplied. This is clear from the meaning of 'the cows' in the good sense as the truths belonging to the interior natural, dealt with in 5198; and from the meaning of 'years' as states, dealt with in 482, 487, 488, 493, 893. There were seven because 'seven' means that which is holy and therefore adds the idea of holiness to the matter under discussion, dealt with in 395, 433, 716, 881, as well as implying a whole period from start to finish, 728. This explains why in the dream seven cows and seven heads of grain were seen, and after that why there were seven years of abundance of corn and seven years of famine. It also explains why the seventh day was made holy, why in the representative Church the seventh year was a sabbatical year, and why after seven times seven years there was a Jubilee.

[2] 'Seven' means things that are holy because of the meanings that numbers have in the world of spirits. Each number there holds some spiritual reality within it. Visual indications of numbers have appeared to me frequently, simple and compound ones, and also on one occasion a long sequence of them, when I have wondered what meanings they possessed. I have been told that they have their origin in conversations held by angels, and that it is customary from time to time to use numbers to express spiritual realities too. These numbers are not seen in heaven but in the world of spirits, where the visual presentation of such things takes place. The most ancients, who were celestial people and who talked to angels, knew all about this, which was why they used numbers to express an evaluation of the Church. The numbers used by them conveyed a general overall idea of matters for which words served to provide a detailed description. The meaning contained within every number did not however continue to be known among the descendants of these people; only the meanings of the simple numbers survived, that is to say, the meanings of two, three, six, seven, eight, twelve, and from these the meanings of twenty-four, seventy-two, and seventy-seven. In particular their descendants knew that 'seven' meant that which was most holy - that is to say, that in the highest sense 'seven' meant the Divine Himself, and in the representative sense the celestial element of love - and that the state of the celestial man was therefore meant by 'the seventh day', 84-87.

[3] It is quite evident from the numbers used plentifully in the Word that numbers mean spiritual realities, such as the following ones in John,

Let him who has intelligence reckon the number of the beast, for it is the number of a man, that is, its number is six hundred and sixty-six. Revelation 13:18.

And elsewhere in the same book,

The angel measured the wall of the holy Jerusalem, a hundred and forty-four cubits, which is the measure of a man, that is, of an angel. Revelation 11:17.

The number one hundred and forty-four is twelve squared and twice seventy-two.