The Bible prophesies the final judgment day. At that time, who will be saved? First, let's look at the cause of the destruction of the whole world.

[Isaiah 24:1-6] See, the LORD is going to lay waste the earth and devastate it; he will ruin its face and scatter its inhabitants- ... The earth is defiled by its people; they have disobeyed the laws, violated the statutes and broken the everlasting covenant. Therefore a curse consumes the earth; its people must bear their guilt.

Likewise, those who do not keep God's law and eternal covenant will be destroyed by God's judgment.
In order to avoid this judgment and destruction, we must keep the law of God and the eternal covenant.
Essentially, the law and the covenant are the same thing.

The law of God = Covenant

This is because the Bible refers to the Ten Commandments as both the law and the covenant.

Then, what is the eternal covenant that must be kept in order to be saved on the day of final judgment?

[Isaiah 55:3] Give ear and come to me; hear me, that your soul may live. I will make an everlasting covenant with you, my faithful love promised to David.

The eternal covenant established to save our souls is the covenant established by David. Who is David in this prophecy? We can find who is David in the Book of Isaiah.

[Isaiah 9:6] For to us a child is born, to us a son is given, and the government will be on his shoulders. And he will be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace. Of the increase of his government and peace there will be no end. He will reign on David's throne and over his kingdom, establishing and upholding it with justice and righteousness from that time on and forever. The zeal of the LORD Almighty will accomplish this.

Jesus fulfilled this prophecy, he was born as a baby. In other words, Jesus is the spiritual King David, the leader and commander of all the nations.
Eternal Covenant = New Covenant
Jesus gives us the New Covenant to save our souls. What is the most important truth within the New Covenant?

[Luke 22:19-20] he took bread, gave thanks and broke it, and gave it to them, saying, "This is my body given for you; do this in remembrance of me." In the same way, after the supper he took the cup, saying, "This cup is the new covenant in my blood, which is poured out for you.

He pointed to the Passover wine and called it the new covenant and said that he wanted to eat the Passover.
The most important truth of the new covenant is the Passover of the new covenant. Therefore, in order to be saved on the Day of Judgment, you must keep the New Covenant Passover.

However, many people who claim to believe in Jesus do not keep the Passover of the new covenant.
In other words, they are breaking the eternal covenant. Will they be saved on the day of final judgment?
They will never be saved. Therefore, we must keep the Passover of the new covenant to be saved on the day of final judgment and enter the eternal kingdom of heaven.