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.

4964. 'Was made to go down to Egypt' means to factual knowledge which the Church possessed. This is clear from the meaning of 'Egypt' as knowledge, or factual knowledge in general, dealt with in 1164, 1165, 1186, 1462. But no explanation of the essential nature of that factual knowledge properly meant by 'Egypt' has been provided as yet. In the Ancient Church there was doctrinal knowledge and there was factual knowledge. Doctrinal knowledge had regard to love to God and charity towards the neighbour, whereas factual knowledge had to do with the correspondences of the natural world with the spiritual world, and with the representations of spiritual and heavenly realities within natural and earthly ones. Such was the factual knowledge of those in the Ancient Church.

[2] Egypt was one of those parts of the world and one of those kingdoms where the Ancient Church also existed, 1138, 1385; but since in that land mainly factual knowledge was handed down from one generation to another, 'Egypt' means factual knowledge in general. This also explains why frequent reference is made to Egypt in the prophetical part of the Word, where that knowledge is meant specifically by 'Egypt'. What is more, the actual magic practised by the Egyptians had its origin in the same knowledge; for they were acquainted with the correspondences of the natural world with the spiritual, and at a later time, after the Church among them had come to an end, they misused these in magical practices. Now because such factual knowledge existed among them - that is to say, knowledge which taught correspondences, and also representatives and meaningful signs - and because this factual knowledge was the servant of the doctrinal teachings of the Church, especially in their understanding of things stated in their Word (for the Word of the Ancient Church was both prophetical and historical, like the Word that exists today, though this is a different Word, see 2686) 'he was made to go down to Egypt' consequently means made to go down to the factual knowledge which the Church possessed.

[3] Because the Lord is represented by 'Joseph' and the words 'Joseph was made to go down to Egypt' are used here, the meaning is that when the Lord was to glorify His Internal Man, that is, make it Divine, He first of all assimilated the factual knowledge possessed by the Church. Then, starting from and using that knowledge He advanced towards things increasingly interior and at length even to those that were Divine. For it pleased Him to glorify or make Himself Divine in conformity with the same kind of order as that by which He regenerates the human being or makes him spiritual, 3138, 3212, 3296, 3490, 4402. That is to say, there is a gradual advance from external ideas, which are known facts and the truths of faith, towards internal ones, which are ideas of charity towards the neighbour and of love to Him. From this one may see what is meant by the following words in Hosea,

When Israel was a boy I loved him, and out of Egypt I called My son. Hosea 11:1.

These words refer to the Lord, see Matthew 2:15.