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.

5335. 'And Joseph was a son of thirty years' means a state when the quantity of remnants was complete. This is clear from the meaning of 'thirty' as a completed number of remnants, dealt with below, and from the meaning of 'years' as states, dealt with in 482, 487, 488, 493, 893. In the Word the number thirty can mean some existence of conflict, or else it can mean a completed number of remnants. The reason why that number has this twofold meaning is that it is arrived at by multiplying five and six, or else by multiplying three and ten. When it is the product of five times six it means some existence of conflict, 2276, because 'five' means some, 649, 4638, 5291, and 'six' conflict, 720, 737, 900, 1709. But when thirty is the product of three times ten it means a completed number of remnants, because 'three' means that which is complete, 2788, 4495, and 'ten' means remnants, 576, 1906, 2284. A composite number implies much the same as the simple ones of which it is the product, 5291. Remnants are the truths joined to good which have been stored away by the Lord in a person's interior parts, see 468, 530, 560, 561, 576, 660, 1050, 1738, 1906, 2284, 5135.

[2] A completed number of remnants is likewise meant by 'thirty' - as it is also by 'sixty', and by 'a hundred' too - in Mark,

The seed which fell into good ground yielded fruit growing up and increasing. One bore thirty-fold, and another sixty, and another a hundred. Mark 4:8, 10.

Each of these numbers, being a multiple of ten, means a completed number of remnants. Also, because no one can be regenerated - that is, permitted to enter into spiritual temptations, by means of which regeneration is effected - until he has received a completed number of remnants, it was therefore laid down that no Levite should carry out any work in the tent of meeting until he was fully thirty years old. Their work or function is also called 'military service', being referred to in Moses as follows,

Take a census of the sons of Kohath from the midst of the sons of Levi - from sons thirty years of age and over, up to sons fifty years of age, everyone coming to perform military service, to do the work in the tent of meeting. Numbers 4:2-3.

Much the same is said regarding the sons of Gershon, and much the same regarding the sons of Merari, in verses 22, 23, 29, 30, and then in verses 35, 39, 43. Of that same chapter in Moses. And something similar is implied where it says that David began to reign when he was a son thirty years of age, 2 Samuel 5:4.

[3] From all this one may now see why the Lord did not make Himself known until He was thirty years of age, Luke 3:23. At that age a completed number of remnants existed with Him, though these remnants which the Lord possessed were ones that He Himself had acquired for Himself. They were also Divine ones and the means by which He united His Human Essence to His Divine Essence and made that Human Essence Divine, 1906. In Him therefore lies the reason why 'thirty years' means a state when the quantity of remnants is complete and why the priests the Levites began to perform their specific functions when they were thirty years old. And because he was to represent the Lord's kingship, David did not begin to reign until he was that same age. For every representative is derived from the Lord, and therefore every representative has reference to Him.