The New Testament began on the cross of Jesus Christ.
The New Testament did not begin with Christ’s birth or His life on earth.It began with His death on the cross.
Hebrews 9 “15 For this reason Christ is the mediator of a new covenant, that those who are called may receive the promised eternal inheritance—now that he has died as a ransom to set them free from the sins committed under the first covenant. 16 In the case of a will, it is necessary to prove the death of the one who made it, 17 because a will is in force only when somebody has died; it never takes effect while the one who made it is living. 18 This is why even the first covenant was not put into effect without blood. “
When Jesus was born, the law was still in effect.
Galatians 4 “4 But when the set time had fully come, God sent his Son, born of a woman, born under the law, 5 to redeem those under the law, that we might receive adoption to sonship.”
This is why Jesus preached the law before His death on the cross, telling the Jews to be righteous by works and be perfect like God to enter heaven.
Matthew 5 “20 For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven….48 Be perfect, therefore, as your heavenly Father is perfect.”
All of Christ’s impossible demands (being perfect, avoiding lust, anger, loving enemies, selling everything, forsaking everything to be saved – was the LAW before the CROSS).
Only Jesus obeyed everything perfectly during the Law.
But on the Cross, the Law was made obsolete. He died for our sins and rose from the dead.
A New Covenant of GRACE was made.
Colossians 2 “13 When you were dead in your sins and in the uncircumcision of your flesh, God made you alive with Christ. He forgave us all our sins, 14 having canceled the charge of our legal indebtedness, which stood against us and condemned us; he has taken it away, nailing it to the cross. “
NOW, we are Righteous APART from the law, but only by FAITH in JESUS CHRIST.
Romans 3 “21 But now apart from the law the righteousness of God has been made known, to which the Law and the Prophets testify. 22 This righteousness is given through faith in Jesus Christ to all who believe. “
We are Righteous without doing a single work but only by FAITH because JESUS did all the work by His death and resurrection to bring GRACE in the New Covenant.
Romans 4 “5 However, to the one who does not work but trusts God who justifies the ungodly, their faith is credited as righteousness. … God will credit righteousness—for us who believe in him who raised Jesus our Lord from the dead. 25 He was delivered over to death for our sins and was raised to life for our justification.”