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.

6091. 'And Jacob blessed Pharaoh' means a heartfelt desire for a joining together and resulting fruitfulness. This is clear from the meaning of 'blessing' here as a heartfelt desire for a joining together - for a joining of truth to factual knowledge in the natural since that is the subject here. 'Blessing has many meanings; in the spiritual sense it includes all things that are good and also those that are blissful. It therefore means being endowed with the good of love and charity, 3185, 4981, also a joining together or conjunction, 3504, 3514, 3530, 3565, 3584, as well as fruitfulness by virtue of the affection for truth, 2846, and a heartfelt desire for someone's happiness, 3185. Here therefore a heartfelt desire for that which is the subject here is meant, namely a desire for a joining together and thus fruitfulness. Fruitfulness follows as a result of the joining together, because once the joining together has been effected good grows and truth multiplies; for the marriage of goodness and truth is then the producer of that fruitfulness. It cannot come about prior to that except as a result so to speak of fornication, the good from which union is spurious, as is the truth. Good from that union is full of self-regard, and truth likewise has the same flavour.