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.

5708. 'Five measures more' means that it was much increased. This is clear from the meaning of 'five' as much, dealt with below; and from the meaning of 'measures' as states of truth received from good, dealt with in 3104. As regards 'five', this is a number which can mean little, or else something, or even much. Whatever its specific meaning, this stems from its relationship with the number of which it is a factor, 5291. When it is a factor of ten, much the same as ten, but in a smaller degree, is implied, five being half the number ten. For just as compound numbers have a similar meaning to the simple ones of which they are the product, 5291, 5335, so do divisors have a similar meaning to the compound numbers they divide, as with the relationship of five to ten, also to twenty, as well as to a hundred, a thousand, and so on. 'Ten' means what is full and complete, see 3107, 4638. 'Five measures more' were given to Benjamin than to the rest of his brothers on account of what was meant by this in the spiritual sense. Ten measures could not be given because that amount would have been far too much. The ancients knew from what had been handed down to them from the Most Ancient Church the meanings that certain numbers carried; they therefore used those numbers whenever something cropped up, the meaning of which could be conveyed by those numbers, as is the case with five here. At other times they employed many other numbers, such as three to mean what was complete from start to finish, seven to mean what was holy, or twelve to mean all things in their entirety.