God knew before He created the world which of the people that He would later create would obey Him until their death.
These people are called FAITHFUL PEOPLE/God's elect. God also knew which of the people would not obey Him until their death. These people who would not obey Him until their deaths are called
FAITHLESS PEOPLE.
So God's elect are those people whom He knew (before the foundation of the world) would still be faithful to Him at the time of their death.
Revelation 2:10
Do not fear what you are about to suffer. Behold, the devil is about to throw some of you into prison, that you may be tested, and for ten days you will have tribulation.
Be faithful unto death, and I will give you the crown of life. rsv
The faithful people are the people who strive to obey God's commandments until they die.
Hebrews 4:11-12
Let us therefore strive to enter that (eternal) rest, that no one fall by the same sort of disobedience. 12 For the word of God is living and active, sharper than any two-edged sword, piercing to the division of soul and spirit, of joints and marrow, and discerning the thoughts and intentions of the heart. rsv
So what will happen to those faithless people whom God knew would either not become obedient or remain obedient to His commandments until they died?
Revelation 21:8
But as for the cowardly, the
faithless, the polluted, as for murderers, fornicators, sorcerers, idolaters, and all liars,
their lot shall be in the lake that burns with fire and brimstone, which is the second death.” rsv
2 Thessalonians 1:7-8
.....when
the Lord Jesus is revealed from heaven
with his mighty angels in flaming fire, 8 inflicting vengeance upon those who do not know God and upon those who do not obey the gospel of our Lord Jesus. rsv
God has always known who His elect are. He predestined these faithful until death people to eternal life/rest. No one can ever snatch these faithful until death people out of His hand. God foreknew that these people would still be abiding in Him (obedient to Him) at the time of their death.
We will have to wait until after we die to find out who His elect/predestined are. We do not know who will still be abiding in Him/faithful to Him/obedient to His commandments at the time of their death.