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.

2559. 'It happened, when God caused me to depart from my father's house' means when He left behind factual knowledge and the appearances that arise from this, together with their delights, meant here by 'father's house'. This is clear from the meaning of 'departing' as leaving behind, and from the meaning of 'house' as good, 2233, here the good that consists in the delight received from the appearances that go with factual knowledge and rational concepts, for all delight appears as good. The reason 'father's house' here means the delights received from factual knowledge and rational concepts, and therefore from the appearances that go with these, is that they are spoken of in reference to Abraham when he departed from his father's house, for at that time, together with his father's house, Abraham worshipped other gods; see 1356, 1992. This explains why the verb in the clause God caused me to depart is plural. This clause, as is also in keeping with the original language, could be rendered, the gods caused me to wander, but because the Lord is represented by Abraham it must be rendered, 'God caused me to depart'. Now it is because the factual knowledge that existed initially with the Lord, and also the rational concepts formed from that knowledge, were human - steeped as they were in what had been inherited from the mother - and so were not purely Divine, that they are represented by 'Abraham's' first state. But how far representations go, see 665, 1097 (end), 1361, 1992.