Revelation 4:6-8
6 And before the throne there was a sea of glass like unto crystal: and in the midst of the throne, and round about the throne, were four beasts full of eyes before and behind.

7 And the first beast was like a lion, and the second beast like a calf, and the third beast had a face as a man, and the fourth beast was like a flying eagle.

8 And the four beasts had each of them six wings about him; and they were full of eyes within: and they rest not day and night, saying, Holy, holy, holy, Lord God Almighty, which was, and is, and is to come.

There has been misconception that there are real beasts worshiping God before his throne in heaven. Why would God choose beasts to worship him? Where is man made in his image? Where is the place of the Church? Do animals sing and talk? Our Lord Jesus said that God is seeking true worshippers who will worship him in spirit and in truth. He is not seeking the worship of animals for animals were not created to worship him.

Who then are the Four Beast before the throne of God? Their identity is unveiled in Revelation 5:9;

Revelation 5:8-9
8 And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, which are the prayers of saints.

9 And they sung a new song, saying, Thou art worthy to take the book, and to open the seals thereof: for thou wast slain, and hast redeemed us to God by thy blood out of every kindred, and tongue, and people, and nation;

Verse 9 says that the four beasts sang a song revealing that they are the redeemed of the Lord. Who are the redeemed of the Lord? The Church of course.

The first beast that looks like a lion is the early church.
The second beast that looks like a calf is the Church during the time it was given to idolatry.
The third beast is like mere men refers to the time of reformation. They are the Church saved but don't have the Holy Spirit. So, they are like mere men.
The fourth beast is like a flying Eagle. This is the present day Church that will witness the rapture which is very near.

The raptured Saints represented by the four beast is in heaven in Revelation Chapter four. They will later be joined by the tribulation Saints in chapter 7.

Revelation 7:9-17
9 After this I beheld, and, lo, a great multitude, which no man could number, of all nations, and kindreds, and people, and tongues, stood before the throne, and before the Lamb, clothed with white robes, and palms in their hands;

10 And cried with a loud voice, saying, Salvation to our God which sitteth upon the throne, and unto the Lamb.

11 And all the angels stood round about the throne, and about the elders and the four beasts, and fell before the throne on their faces, and worshipped God,

12 Saying, Amen: Blessing, and glory, and wisdom, and thanksgiving, and honour, and power, and might, be unto our God for ever and ever. Amen.

13 And one of the elders answered, saying unto me, What are these which are arrayed in white robes? and whence came they?

14 And I said unto him, Sir, thou knowest. And he said to me, These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.

15 Therefore are they before the throne of God, and serve him day and night in his temple: and he that sitteth on the throne shall dwell among them.

16 They shall hunger no more, neither thirst any more; neither shall the sun light on them, nor any heat.

17 For the Lamb which is in the midst of the throne shall feed them, and shall lead them unto living fountains of waters: and God shall wipe away all tears from their eyes.

It is impossible for new souls who were never born again before the rapture to be born again after the rapture because the Holy Spirit will no longer be on earth that period.

But those who are born again but left behind will still be saved if they repent of their sins and hold on to their faith. However they will all be persecuted to death.