Considering that God's chosen were foreknown and predestined to be conformed to the image of His Son, yet seeing that many are called but few chosen (Matthew 20:16; 22:14), we are left wondering who was foreknown and who was predestined.
A safe approach to this is to understand that predestination applies to the church as a whole group. In other words, in the beginning God knew that He would raise up the church to do its work in the world and to nurture His called-out ones.
More recently, we have understood this to be far more specific. The Bible indicates that God foreknew several individuals at least from before their births (Isaac, Jacob, Samson, David, Solomon, Jeremiah, John the Baptist, etc.), so His foreknowledge includes specific people. It makes perfect sense that God would want certain individuals to perform in a particular way when He wanted special things done, as that is a pattern God has used in the past.
However, God's foreknowledge and predestination “to adoption as sons, . . . according to the good pleasure of His will” (Ephesians 1:5) is not an absolute guarantee of salvation and eternal life. The Bible is unambiguous in its assertions that a person can lose his salvation (see, for instance, Hebrews 2:1-3; 3:12; 4:1; 6:4-8; 10:26-31). If an individual could not lose his salvation, then why does God provide so many passages warning us of the possibility?
God is not a liar and does not warn without cause. These warnings are given because God has cause to give them! While God is sure of His ability to work out the salvation of every person He calls, each person has his part to play, that is, he must believe and cooperate with God throughout the sanctification process, growing in the image of His Son, Jesus Christ. This is why the apostle Paul urges us to “work out your own salvation with fear and trembling; for it is God who works in you both to will and to do for His good pleasure” (Philippians 2:12-13). In other words, though God chooses us, we must also choose Him.
An individual's sins could cause him to lose this awesome opportunity. Yes, God is eager to forgive all our sins and set us back on the path of righteousness, but that act of mercy cannot begin if we do not seek forgiveness and repentance from Him. A sin is unpardonable if one refuses to ask God to pardon it.
A person can also turn away from God so willfully that he becomes a rebel against God, repudiating his former belief and “trampl[ing] the Son of God underfoot” (Hebrews 10:29). Christ's sacrifice does not apply in such a case because it cannot be applied twice to the same person. As the writer of Hebrews says, this is considering the blood of the covenant, Christ's own blood, to be common and an insult to the Spirit of grace.
Further, why would He reveal that there will be a Lake of Fire for the incorrigibly wicked if it would not be needed? Certainly, the Devil and his demons will be cast into it, as well as the Beast and False Prophet (Revelation 20:10), but Hebrews 10:26-27 indicates that this is also the fate of those who “sin willfully after receiv[ing] the knowledge of the truth” (see also Hebrews 6:8). By the way, the Lake of Fire imagery stands behind Jesus' illustrations of Gehenna fire as well as the fate of the man not wearing a wedding garment: “outer darkness” and “weeping and gnashing of teeth.”
This is why God warns us so often and so urgently in the pages of the Bible—because He does not want to lose those He has called to salvation!
John O. Reid (1930-2016)
Many Are Called, Few Are Chosen