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.

4976. 'And ministered to him' means that factual knowledge was assigned to its own good. This is clear from the meaning of 'ministering' as serving by supplying what another has need of, in this case as being assigned to since the subject is natural good to which factual knowledge is to be assigned. 'Ministering' is also used to describe known facts, for in the Word a minister and a servant mean factual knowledge or natural truth because this is subservient to good as its lord. Factual knowledge stands in relation to delight present in the natural man - or what amounts to the same, natural truth stands in relation to its good - in exactly the same way as water does to bread, or drink to food. Water or drink enables bread or food to be dissolved, and once dissolved to be conveyed into the blood, from which it passes into all parts around the body and nourishes them. Without the water or drink the bread or food is not broken down into extremely small particles and carried around the body to fulfill its purpose.

[2] The same applies to factual knowledge in relation to delight, or truth in relation to good. That being so, good longs for and desires truth, and does so because of the purpose such truth can fulfill by ministering to it and serving it. Food and drink also correspond to these. No one in the next life is nourished by any natural food or natural drink, only by spiritual food and spiritual drink, spiritual food being good, and spiritual drink truth. This is why, when bread or food is mentioned in the Word, angels understand spiritual bread or food, which is the good of love and charity; and when water or drink is mentioned they understand spiritual water or drink, which is the truth of faith. From this one may see what the truth of faith without the good of charity is, and also what kind of nourishment the former without the latter is able to supply to the internal man; that is to say, it is like the nourishment supplied by water or drink alone without bread or food. It is well known that a person fed on water or drink alone wastes away and dies.