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.

2636. 'Abraham was a son a hundred years old' means a complete state of union. This is clear from the meaning of 'a hundred' as that which is complete, dealt with immediately below, and from the meaning of 'years' as state, dealt with in 482, 487, 488, 493, 893, here a state of union. What a complete state is of the Lord's Divine united to His Human, or what amounts to the same, united to the Rational - for the human has its beginnings in the inmost part of the rational, 2106, 2194 - is not easy to express in a way that can be understood, though it can nevertheless be illustrated by the things which with man are called a complete state when he is being reformed and regenerated.

[2] It is well known that a person cannot be regenerated except in adult years, for not until then is he able to exercise reason and judgement and in so doing to receive good and truth from the Lord. Before entering that state he is being prepared by the Lord through the implantation of such things as can serve him as the soil for receiving the seeds of truth and good. Implanted thus are many states of innocence and charity, also cognitions of good and truth, and consequently thoughts. This implantation occurs during many years before his regeneration takes place. When a person has been endowed with these things and so has been prepared, his state is now said to be complete, for the things that are interior have been arranged ready to receive. All those things with a person which the Lord grants him prior to regeneration and by means of which he is regenerated are called remnants, which in the Word are meant by the number ten, 576, 1738, 2284, and also by a hundred when the state for regeneration is complete, 1988.

[3] These things that are so with man may serve to illustrate what is meant by a complete state of the Human united to the Divine in the Lord. That is to say, they may illustrate the state when the Lord by His own power - through the conflicts brought about by temptations and through victories, and through the powers of Divine wisdom and intelligence - gathered to Himself within the Human, that is, within the Rational, so much of the Divine that He was able to unite the Divine itself to the Divine acquired within the Rational. And it was to represent this state that, even though Abraham had spent many years in the land of Canaan, Isaac was not born to him until he was a hundred years old. These are the arcana contained within the number 'a hundred years', which was Abraham's age.

[4] That the number 'a hundred' means that which is complete may also be seen from other places in the Word, as in Isaiah,

No more will there be from it an infant of days, nor an old man who has not completed his days, for the child will die a son a hundred years old, and the sinner a son a hundred years old will be accursed. Isaiah 65:20.

Here 'a hundred' clearly stands for that which is complete, for it is said, 'No more will there be an infant of days, nor an old man who has not completed his days', and, a child and a sinner will be 'a hundred years old', that is, a time when his state is complete.

[5] In Matthew,

Everyone who has left houses or brothers or sisters or father or mother or wife or children or fields, for My name's sake, will receive a hundredfold and will be allotted the inheritance of eternal life. Matthew 19:29; Mark 10:29-30.

Here 'a hundredfold' stands for that which is complete, otherwise described as 'good measure, pressed down, shaken together, and running over', in Luke 6:38.

[6] In Luke,

Some seed fell on good ground, and when it had grown up it brought forth fruit a hundredfold. Luke 8:8; Matthew 13:8, 23; Mark 4:20.

Here also 'a hundred' stands for that which is complete, a number which would not have been mentioned unless it had had that meaning. A similar meaning exists in the parable about the debtors, where the Lord says that one owed a hundred baths of oil and the other a hundred cors of wheat, Luke 16:5-7. The same applies in other places where a hundred is mentioned. It is similar with a thousand, regarding which number, see 2575.