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.

3464. 'And pointed out to him the reasons for the well which they had dug; and they said to him, We have found water' means interior truths obtained by means of these. This is clear from the meaning of 'a well' as the Word, dealt with in 3424, and from the meaning of 'water' as truths, dealt with in 2702, that is to say, truths drawn from the Word. 'Pointing out to him the reasons for the well which they had dug' accordingly means concerning the Word, the source of matters of doctrine; 'and they said to him, We have found water' means that it is in these, that is to say, in matters of doctrine, that interior truths reside; for as stated above, all matters of doctrine drawn from the literal sense of the Word include interior truths within them. For the literal sense of the Word is like a well with water in it, in that every single thing in the Word holds within itself the internal sense, which resides also in matters of doctrine drawn from the Word.

[2] The situation with matters of doctrine drawn from the literal sense of the Word is that when anyone possesses them and at the same time lives according to them a correspondence exists within himself. For the angels who reside with him are alive to the interior truths when he is alive to the exterior; and in this way he has communication with heaven by means of matters of doctrine, though this is conditioned by how good a life he leads. For example, when at the Holy Supper this person in simplicity thinks about the Lord from the words 'This is My body' and 'This is My blood' the angels residing with him have in mind love to the Lord and charity towards the neighbour; for love to the Lord corresponds to the Lord's body and to the bread, while charity towards the neighbour corresponds to His blood and to the wine, 1798, 2165, 2177, 2187. This being the nature of the correspondence, there flows from heaven by way of the angels into that holiness present with the person at that time an affection which he receives according to the good within his life.

[3] Actually angels dwell with every person in the affection that belongs to his life, and so in the affection for the matters of doctrine according to which he lives, but never in the matters of doctrine with which his life is at variance. If his life is at variance with them, as it is if his affection is to gain position and wealth for himself by means of matters of doctrine, the angels in that case depart and spirits from hell dwell in that affection. These either instill their confirmations into him that favour self and the world - thus a false persuasion, which is such that he does not care at all whether a thing is true or false, provided people's attention is drawn to himself - or they take away all faith, in which case the doctrine on that person's lips is merely a sound prompted and fashioned by the fire of those loves.