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.

4249. 'And Jacob was exceedingly afraid, and was distressed' means the state when it is being changed. This is clear from the fact that fear and distress are the first stage in temptations, and that they are precursors to the turning round or the change taking place within a state. The arcana which lie deeper still within these details - that is to say, Esau's coming to meet Jacob with four hundred men, and Jacob's consequent fear and distress - cannot be explained easily and intelligibly since they are rather more internal ones. Let just this one be brought forward here. When good takes up the first position and subordinates truths to itself, as happens when a person undergoes spiritual temptations, the good which flows in from the interior is accompanied by very many truths which have been stored away in the person's interior man. Those truths cannot come into focus and be seen by him until good is playing the leading role, for when this happens the natural starts to receive light from good, and it is apparent to him which things in the natural agree and which ones do not. And this is what gives rise to the fear and distress that are the precursors to spiritual temptation. For spiritual temptation acts upon the conscience, which is an attribute of the interior man, and therefore when entering such temptation a person does not know the origin of his fear and distress. But the angels present with him know it full well. Indeed temptation has its origin in angels' maintenance of the person in goods and truths, while evil spirits maintain him in evils and falsities.

[2] The things that occur among the spirits and angels present with a person are perceived by him purely as things going on within himself. For while he lives in the body and does not believe that everything within him flows in from somewhere other than himself, he imagines that the causes of the things that go on within him do not lie outside himself but that all causes lie within him and are his own - which is not in fact the case. For whatever a person thinks and what he wills, that is, all his thought and all his affection, originate either in hell or in heaven. When he thinks and wills anything evil and as a consequence takes delight in falsities, let him realize that his thoughts and affections originate in hell; but when he thinks and wills anything good and as a consequence takes delight in truths, let him realize that these originate in heaven, that is, in the Lord by way of heaven. But the person's thoughts and affections more often than not take on a different outward appearance. A conflict between evil spirits and angels, for example, arising from the things in one who is to be regenerated, takes on the different outward appearance of fear and distress, and of temptation.

[3] These matters are bound to seem paradoxes to man, for almost every member of the Church at the present day believes that all the truth he thinks, and the good he wills and does, originate in himself, even though he says something other than that when speaking from doctrine taught by faith. Indeed his nature is such that if anyone told him that spirits from hell exist who flow into his thought and will when he thinks and wills anything evil, and angels from heaven when he thinks and wills anything good, he would be dumbfounded at anyone putting forward such an idea, for he would say that he can feel the life within himself and that he thinks from himself and wills from himself. His belief is based on that feeling and not on what doctrine teaches. Yet that doctrine is true and such feeling deceptive. This I have been allowed to know from almost uninterrupted experience lasting several years now, and to know it in such a way as to leave me in no doubt whatsoever.