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.

28. Verse 10 And God called the dry land Earth, and the gathering together of the waters He called Seas; and God saw that it was good.

It is very common in the Word for 'waters' to mean cognitions and facts, and consequently for 'seas' to mean a gathering together of them, as in Isaiah,

The earth will be full of the knowledge of Jehovah as the waters covering the sea. Isaiah 11:9.

And in the same prophet, with reference to a lack of cognitions and facts,

The waters will dry up from the sea, the river will be parched and dry, and the streams will diminish. Isaiah 19:5-6.

In Haggai, with reference to a new Church,

I will shake the heavens and the earth, and the sea and the dry land; and I will shake all nations, and the desire of all nations will come, and I will fill this house with glory. Haggai 2:6-7.

And with reference to someone who is to be regenerated, in Zechariah,

There will be one day - it is known to Jehovah - not day and not night, for at evening time there will be light; and on that day living waters will flow out from Jerusalem, part of them to the eastern sea, and part of them to the western sea. Zechariah 14:7-8.

In David where the person is described who, having been vastated, is to be regenerated, and to worship the Lord, Jehovah does not despise His bound ones. Heaven and earth will praise Him, the seas and everything that creeps in them! Psalms 69:33-34.

That 'the earth' means that which receives is seen in Zechariah,

Jehovah is He who stretches out the heavens, and founds the earth, and forms the spirit of man within him. Zechariah 12:1.