A cornerstone of Christian doctrine it the literal death and resurrection of Jesus Christ--fully human and fully God—as a propitiation for the sin of humanity—past, present, and future—and available simply (and only) by believing God's promise of salvation and eternal life through Christ, the “Holy One” of the Old Testament, and the “Word” of the New Testament. The full doctrine is this:
(A) Human beings can never be free of sin on their own, and thus,
(B) ... are deserving of death (instead of everlasting life).
(C) Because God the Father must turn his face away from sin, it is impossible for people who are sinners to approach God on their own merits.
(D) In order to atone for the imperfect (sin) nature of humans, God came to earth as the man Jesus, to be fully God and fully human, and to live a sinless life,
(E) ... so that he could die a sinner's death as a substitutionary death for the sin of humanity.
(F) The atonement is "free" if the person acknowledges the sin and the need for atonement and identifies with the death of Jesus the Christ (messiah).
(G) The physical, literal resurrection of Jesus, to eternal life, allows the person who identified with His death also to identify with (and to achieve) His eternal life.
There are numerous scripture passages that elucidate this foundational doctrine. Those that I think highlight the essentials of the doctrine are included below, along with the letter of the sub-doctrine indicated above. I include references from the Old Testament, written long before the birth of Jesus, and from the New Testament—which includes the four Gospels, which recount the life and teachings of Jesus while he was on earth, and the epistles and books that were written long after Jesus' death and resurrection.
~~~
(A) Humans are sinful:~
Psalm 14:2-3 (Old Testament)
The LORD looks down from heaven upon the children of men,
To see if there are any who understand, who seek God.
They have all turned aside,
They have together become corrupt;
There is none who does good,
No, not one.
~
Ecclesiastes 7:20 (Old Testament)
For there is not a just man on earth who does good
And does not sin.
~
(B) The penalty of sin is death:~
Genesis 2:16-17 (Old Testament)
And the LORD God commanded the man, saying, “Of every tree of the garden you may freely eat; but of the tree of the knowledge of good and evil you shall not eat, for in the day that you eat of it you shall surely die.”
~
Ecclesiastes 12:14 (Old Testament)
For God will bring every work into judgment,
Including every secret thing,
Whether good or evil.
~
Romans 5:12-13
Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned.
~
Romans 6:23a
For the wages of sin is death....
~
Leviticus 1:4 (Old Testament)
Then he shall put his hand on the head of the burnt offering, and it will be accepted on his behalf to make atonement for him.
~
(C) God turns away from sin and sinners:~
Isaiah 59:2 (Old Testament)
But your iniquities have separated you from your God;
And your sins have hidden His face from you,
So that He will not hear.
~
Deuteronomy 23:14 (Old Testament)
For the LORD your God walks in the midst of your camp...; therefore your camp shall be holy, that He may see no unclean thing among you, and turn away from you.
~
Isaiah 64:5b-6a,7b (Old Testament)
You are indeed angry, for we have sinned—
In these ways we continue;
And we need to be saved.
But we are all like an unclean thing,
And all our righteousnesses are like filthy rags; ...
For You have hidden Your face from us,
And have consumed us because of our iniquities.
~
(D) Christ (Jesus), the Word or Right Hand of God, was present before the world began, created the world, and later came to earth as the Light of the world, fully human and fully God:~
John 1:1-4,10-12,14
In the beginning was the Word, and the Word was with God, and the Word was God.
He was in the beginning with God.
All things were made through Him, and without Him nothing was made that was made.
In Him was life, and the life was the light of men....
He was in the world, and the world was made through Him, and the world did not know Him.
He came to His own, and His own did not receive Him.
But as many as received Him, to them He gave the right to become children of God, to those who believe in His name....
And the Word became flesh and dwelt among us, and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth.
~
1 John 5:7For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one.
~
(E) Jesus, through His death, is the perfect atonement for the sin of humanity:~
Isaiah 53:5 (Old Testament)
But He was wounded for our transgressions,
He was bruised for our iniquities;
The chastisement for our peace was upon Him,
And by His stripes we are healed.
~
Hebrews 9:11-12
But Christ came as High Priest of the good things to come, with the greater and more perfect tabernacle not made with hands, that is, not of this creation.
Not with the blood of goats and calves, but with His own blood He entered the Most Holy Place once for all, having obtained eternal redemption.
~
Hebrews 10:10b-12,14
we have been sanctified through the offering of the body of Jesus Christ once for all.
And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins.
But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, ...
For by one offering He has perfected forever those who are being sanctified.
~
(F) Who is eligible for forgiveness through Jesus' atonement?:~
Romans 10: 9-10,13
that if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved.
For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation....
For “whoever calls on the name of the LORD shall be saved.”
~
John 3:16-17For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life.
For God did not send His Son into the world to condemn the world, but that the world through Him might be saved.
~
(G) Why is the resurrection necessary? (Why not just the atoning sacrifice?):~
(See http://www.christianitytoday.com/le/currenttrendscolumns/leadershipweekly/cln50321.html for an excellent discussion of this.)~
1 Corinthians 15:13-15
But if there is no resurrection of the dead, then Christ is not risen.
And if Christ is not risen, then our preaching is empty and your faith is also empty.
Yes, and we are found false witnesses of God, because we have testified of God that He raised up Christ, whom He did not raise up—if in fact the dead do not rise.
~
1John5:12
He who has the Son has life; he who does not have the Son of God does not have life.
~
1Peter3: 18For Christ also suffered once for sins, the just for the unjust, that He might bring us to God, being put to death in the flesh but made alive by the Spirit,
~
[Note: All scripture passages included here are taken from the New King James Version of the Bible. There are many excellent, accurate translations. I happen to like this one, personally.]~