Unconditional election is elegantly and concisely defined in the Belgic Confession, article 16:
We believe that—all Adam’s descendants having thus fallen into
perdition and ruin by the sin of Adam—God showed himself to be as he
is: merciful and just.
God is merciful in withdrawing and saving from this perdition those
who, in the eternal and unchangeable divine counsel, have been elected
and chosen in Jesus Christ our Lord by his pure goodness, without any
consideration of their works.
God is just in leaving the others in their ruin and fall into which
they plunged themselves.
You can read fuller definitions and defenses of the doctrine in the first section of the Canons of Dort and in chapter 3 of the Westminster Confession of Faith, but the essentials can be identified pretty clearly:
God could justly condemn all men for their sins, but he chose to elect some to salvation and elect others to their due condemnation.
God chose the elect for salvation not based on anything good he foresaw in them, but according to the good pleasure of his will.
God's decree of election is eternal and unchangeable.
Romans 8, 9, and 11 spell out the doctrine possibly more clearly than anywhere else. Romans 8:28-30 lays out what is often called the "golden chain of salvation":
And we know that all things work together for good for those who love
God, who are called according to his purpose, because those whom he
foreknew he also predestined to be conformed to the image of his Son,
that his Son would be the firstborn among many brothers and sisters.
And those he predestined, he also called; and those he called, he also
justified; and those he justified, he also glorified.
Arminians believe that "foreknew" means that God first foresaw who would love God, and then predestined them to salvation. But Calvinists believe that this is absurd: to love God, one first has to "be conformed to the image of his Son." So they believe that foreknowledge refers to God "knowing" or loving his people from eternity. This sense of "know" can be seen in Jeremiah 1:5:
Before I formed you in your mother's womb I chose [Hebrew: "knew"]
you. Before you were born I set you apart. I appointed you to be a
prophet to the nations.
The inseparability of the links in the "golden chain" can be demonstrated by 1 John 2:19:
They went out from us, but they did not really belong to us, because
if they had belonged to us, they would have remained with us. But they
went out from us to demonstrate that all of them do not belong to us.
The eternality of the election decree can also be seen in these verses:
For he chose us in Christ before the foundation of the world that we
may be holy and unblemished in his sight in love. He did this by
predestining us to adoption as his sons through Jesus Christ,
according to the pleasure of his will— to the praise of the glory of
his grace that he has freely bestowed on us in his dearly loved Son.
2 Thessalonians 2:13-14
But we ought to thank God always for you, brothers and sisters loved
by the Lord, because God chose you from the beginning for salvation
through sanctification by the Spirit and faith in the truth. 14 He
called you to this salvation through our gospel, so that you may
possess the glory of our Lord Jesus Christ.
When the Gentiles heard this, they began to rejoice and praise the
word of the Lord, and all who had been appointed for eternal life
Romans 9 has a lot to say on the subject of election:
6 It is not as though the word of God had failed. For not all those
who are descended from Israel are truly Israel, 7 nor are all the
children Abraham’s true descendants; rather “through Isaac will your
descendants be counted.” 8 This means it is not the children of the
flesh who are the children of God; rather, the children of promise are
counted as descendants. 9 For this is what the promise declared:
“About a year from now I will return and Sarah will have a son.” 10
Not only that, but when Rebekah had conceived children by one man, our
ancestor Isaac— 11 even before they were born or had done anything
good or bad (so that God’s purpose in election would stand, not by
works but by his calling)— 12 it was said to her, “The older will
serve the younger,” 13 just as it is written: “Jacob I loved, but Esau
So not all members of national Israel are part of the true Israel, and those of the true Israel are chosen before they are even born. Paul continues:
14 What shall we say then? Is there injustice with God? Absolutely
not! 15 For he says to Moses: “I will have mercy on whom I have mercy,
and I will have compassion on whom I have compassion.” 16 So then, it
does not depend on human desire or exertion, but on God who shows
mercy. 17 For the scripture says to Pharaoh: “For this very purpose I
have raised you up, that I may demonstrate my power in you, and that
my name may be proclaimed in all the earth.” 18 So then, God has mercy
on whom he chooses to have mercy, and he hardens whom he chooses to
So according to God's good pleasure he has mercy on some and leaves others in their wickedness. This is confirmed in other verses:
The Lord works everything for its own ends—even the wicked for the day
1 Peter 2:8b
They stumble because they disobey the word, as they were destined to
This comports well with how Paul continues his argument in Romans 9:
21 Has the potter no right to make from the same lump of clay one
vessel for special use and another for ordinary use? 22 But what if
God, willing to demonstrate his wrath and to make known his power, has
endured with much patience the objects of wrath prepared for
In Romans 11, Paul begins by speaking of the "remnant" that God preserved during the time of Elijah:
5 So in the same way at the present time there is a remnant chosen by
grace. 6 And if it is by grace, it is no longer by works, otherwise
grace would no longer be grace. 7 What then? Israel failed to obtain
what it was diligently seeking, but the elect obtained it. The rest
were hardened, 8 as it is written, “God gave them a spirit of stupor,
eyes that would not see and ears that would not hear, to this very
day.” [Quoting Deuteronomy 29:4]
9 And David says, “Let their table become a snare and trap, a
stumbling block and a retribution for them; 10 let their eyes be
darkened so that they may not see, and make their backs bend
continually.” [Quoting Psalm 69:22-23]
As we've already seen, the idea of God's salvation not being based on any good that he foresees goes back to the Old Testament. God says of Israel:
It is not because you were more numerous than all the other peoples
that the Lord favored and chose you—for in fact you were the least
numerous of all peoples. Rather it is because of his love for you and
his faithfulness to the promise he solemnly vowed to your ancestors
that the Lord brought you out with great power, redeeming you from the
place of slavery, from the power of Pharaoh king of Egypt.
I made myself available to those who did not ask for me; I appeared to
those who did not look for me. I said, ‘Here I am! Here I am!’ to a
nation that did not invoke my name.
It's all over the New Testament as well. Faith is seen as a gift:
You did not choose me, but I chose you and appointed you to go and
bear fruit, fruit that remains, so that whatever you ask the Father in
my name he will give you.
44 No one can come to me unless the Father who sent me draws him, and
I will raise him up at the last day. ... 64 But there are some of you
who do not believe. ... 65 Because of this I told you that no one can
come to me unless the Father has allowed him to come.
2 Timothy 1:9
He is the one who saved us and called us with a holy calling, not
based on our works but on his own purpose and grace, granted to us in
Christ Jesus before time began.
2 Peter 1:1
From Simeon Peter, a slave and apostle of Jesus Christ, to those who
through the righteousness of our God and Savior, Jesus Christ, have
been granted a faith just as precious as ours.
For it has been granted to you not only to believe in Christ but also
to suffer for him.
We've already seen verses that speak of "hardening" the reprobate. God actively hides knowledge from some, just as he actively reveals it to others, all for his glory:
At that time Jesus said, “I praise you, Father, Lord of heaven and
earth, because you have hidden these things from the wise and
intelligent, and revealed them to little children. Yes, Father, for
this was your gracious will.
You have been given the opportunity to know the secrets of the kingdom
of heaven, but they have not.
1 Corinthians 1:26-31
Think about the circumstances of your call, brothers and sisters. Not
many were wise by human standards, not many were powerful, not many
were born to a privileged position. But God chose what the world
thinks foolish to shame the wise, and God chose what the world thinks
weak to shame the strong. God chose what is low and despised in the
world, what is regarded as nothing, to set aside what is regarded as
something, so that no one can boast in his presence. He is the reason
you have a relationship with Christ Jesus, who became for us wisdom
from God, and righteousness and sanctification and redemption, so
that, as it is written, “Let the one who boasts, boast in the Lord.”