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.

3513. 'And I will eat' means in that way making it its own. This is clear from the meaning of 'eating' as being made one's own, dealt with in 2187, 2343, 3168, 3503. It is made its own when, by means of forms of pleasantness and delight, truths, that is, cognitions of good and truth, are instilled into the natural; and when these truths are allied to the good in the natural, communication is effected with the truth and good of the rational and so with the rational itself. It is this communication that the expression 'being made one's own' is used to describe, for those truths belong to the rational within the natural. Indeed truths in the rational are related to those in the natural in the way that individual parts are related to their general wholes. It is well known that a general whole is the product of its individual parts and that without the individual parts no general whole can be produced. It is the general whole produced from the individual parts belonging to the rational that is manifested in the natural. And being a general whole it takes a different form, doing so according to the order of the individual constituent parts, and so according to the form that results. If it is the more specific and the consequent individual parts of celestial good and spiritual truth that give form to the general whole within the natural, then it is a celestial and spiritual form that is presented, and something of heaven is represented as a kind of image in the specific parts constituting the general whole. But if the more specific and the individual parts which give form to the general whole within the natural do not consist of good and truth but of evil and falsity, something of hell is in that case represented as a kind of image in the specific parts constituting the general whole.

[2] Such are the things meant by eating and drinking in the Holy Supper, where again eating and drinking mean making one's own; that is to say, 'eating' means making good one's own and 'drinking' making truth one's own. If good, that is to say, love to the Lord and charity towards the neighbour, gives form to the internal or rational man, and by way of this rational man gives form to a corresponding external or natural man, the person becomes in particular and in general an image of heaven, and therefore an image of the Lord. But if contempt for the Lord and for the good and truth of faith, and hatred towards the neighbour give form to the rational man, the person becomes in particular and in general an image of hell - the more so if at the same time he eats and drinks in a holy manner, for profanation then results. Consequently people who eat and drink worthily make eternal life their own, whereas those who do so unworthily make [eternal] death their own.