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.

10238. 'And put water in it' means the truths of faith by means of which purification in the natural is accomplished. This is clear from the meaning of 'water' as the truths of faith, dealt with in 28, 739, 2702, 3058, 3424, 4976, 5668, 8568, 9323; and from the meaning of 'the laver' as the natural, dealt with above in 10235. Anyone who does not know that 'water' means the truths of faith will fail to grasp the meaning of very many statements in the Word, such as unless a person is born of water and the spirit he cannot enter the kingdom of God, John 3:5. Those who take water here to mean nothing other than water think that the water of baptism is the means by which a person is regenerated. But in fact the water does nothing towards regeneration, only the truth of faith and the good of love do so; for water washes away solely dirt that is on the body and by no means evils present in the heart.

[2] Anyone who does not know that 'water' means the truths of faith cannot know what baptism means, either. He thinks that the external act saves a person, when in fact the external act does not accomplish anything, only the inner reality meant by it, namely regeneration by means of the truths of faith. Baptism makes people belonging to the Church different from everyone else throughout the world, because unlike those outside the Church they are able to be regenerated by means of the truths of faith. For the Word, which contains the truths of faith, exists within the Church.

[3] Nor can anyone who does not know that 'water' means the truths of faith know what is meant in Genesis 1:6-10 by the waters above the expanse and the waters under the expanse. Truths of faith within the internal man are meant by 'the waters above the expanse', and truths of faith in the external by 'the waters under the expanse'; for the subject in that chapter is the new creation, thus the regeneration, of members of the Most Ancient Church.

[4] Nor can anyone who does not know that 'water' means the truths of faith know what is meant by 'water' in John,

He who drinks of the water that I shall give will never thirst. But the water that I shall give will become in him a spring of water welling up into eternal life. John 4:13-14.

And in Isaiah,

The poor and the needy are seeking water, but there is none; their tongue is parched with thirst. I will open streams on the sloping heights, and I will place springs in the midst of valleys; I will make the wilderness into a pool of water, and the dry land into wellsprings of water. Isaiah 41:17-18.

And again in the same prophet,

They will not thirst. He will make water flow for them from the rock; and He will cleave the rock so that water flows out. Isaiah 48:20-21.

And in very many other places. But see what has been stated and shown previously on these matters,

Purification from evils and falsities is accomplished by means of the truths of faith, 2799, 5954(end), 7044, 7918, 9089, 10229.

So too is regeneration, see the places referred to in 9959.

'Baptism' means regeneration by means of the truths of faith, 4255, 5120(end), 9089.

Purification is accomplished within the natural, 3147, 9572.

And so is regeneration, see the places referred to in 9325.