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.

9230. 'And you shall not eat flesh torn in the field' means that falsified good of faith must not be joined [to oneself]. This is clear from the meaning of 'flesh' as good, dealt with in 7850, 9127; from the meaning of 'the field' as the Church in respect of good, thus the Church's good, dealt with in 2971, 3766, 7502, 7571, 9139, 9141; from the meaning of 'torn' as something destroyed by falsities, thus also something falsified, dealt with in 5828; and from the meaning of 'eating' as making one's own and joining [to oneself], dealt with in 2187, 3168, 3513 (end), 3596, 4745, 5643, 8001. From these meanings it is evident that 'you shall not eat flesh torn in the field' means that the Church's good, or the good of faith, if it has been falsified, is not to be made one's own or joined [to oneself].

[2] A brief statement must be made here about what the good of faith is and what the truth of faith is. The good of faith is a term that denotes everything of the Church that has to do with life and service inspired by teachings of the Church that compose its faith, in short, everything that has to do with willing those things and doing them in a spirit of obedience; for the Church's truths of faith become, through people's willing them and doing them, forms of good. But the truth of faith is a term that denotes everything which does not as yet have useful service as its end in view or does not exist for the sake of its use in life. Consequently it is something a person comes to know and retain in the memory, then grasps with his understanding, and goes on to teach. As long as the Church's truths go no further than the understanding they are merely items of knowledge and known facts, and in contrast to forms of good stand outside the person himself. For the human memory and understanding are like the hall outside a room, and the will is so to speak the actual room, the will being the person himself. This shows what the truth of faith is and what the good of faith is. But the good that a person does in the first state, while he is being regenerated, is called the good of faith, whereas the good that he does in the second state, which is when he has been regenerated, is called the good of charity. When therefore a person doing good is governed by the good of faith, he does good in a spirit of obedience; but when someone doing good is governed by the good of charity, he does good out of affection. Regarding those two states with a person who is being regenerated, see 7923, 7992, 8505, 8506, 8510, 8512, 8516, 8643, 8648, 8658, 8685, 8690, 8701, 9224, 9227.