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.

1044. 'And it will be for a sign of the covenant between Me and the earth' means a token of the Lord's presence in charity, 'the earth' here being a person's proprium. This is clear from what has been stated already. That 'the earth' means a person's Proprium is clear from the internal sense and from the whole train of thought. Above it was stated that 'this is the sign of the covenant between Me and you and every living soul that is with you' meant whatever has been regenerated; but here the wording is different - 'it will be for a sign of the covenant between Me and the earth'. From this, and also from the repetition of 'sign of the covenant', it is evident that something different is meant here, and indeed that 'the earth' is that which has not been regenerated, and which is incapable of being, namely the will part of a person's proprium.

[2] When somebody is regenerate he belongs to the Lord so far as the understanding Part of his mind is concerned but belongs to himself so far as the will part of it is concerned. These two parts in the spiritual man are opposed to each other. But although the will part of a person's proprium is opposed, its continuing presence is nevertheless inevitable. Indeed all the obscurity in the understanding part, that is, all the thickness of his cloud, originates there. It is constantly flowing in from there, and in the measure it flows in so the cloud in the understanding part thickens; but in the measure it is taken away, the cloud thins out. This is why 'the earth' here means a person's proprium. That 'the earth' means the bodily part of man's nature as well as having many other meanings has been shown already.

[3] The relationship between those two parts is like two parties who were first of all joined together by a covenant of friendship - as will and understanding were in the member of the Most Ancient Church - and then the friendship was broken off and hostility arose, as happened when man corrupted totally the will part of him. After that, when the covenant is renewed, the hostile part presents itself as though the covenant were with it. But no covenant is made with it because it is utterly opposed and contrary. It is made instead with that which flows in from it, as has been stated, that is, with the understanding part of the proprium. The sign or token of the covenant is this, that to the extent the Lord is present in the understanding part of the proprium the will part of it will be taken away. The relationship between the two is just like that of heaven and hell. The understanding part of a regenerate person, by virtue of the charity in which the Lord is present, is heaven, while the will part of him is hell. To the extent the Lord is present in heaven, hell is removed; for when he subsists from himself man is in hell, but when he does so from the Lord he is in heaven. Man is constantly being raised up from hell into heaven, and so far as he is raised up his hell is taken away from him. The sign or token therefore that the Lord is present rests in the fact that man's own will is taken away. The possibility of that removal is achieved by means of temptations and many other means of regeneration.