Jesus's finished work and the action of faith in our hearts
Sin separates from God
Isaiah 59:2
But your iniquities have separated you from your God;
And your sins have hidden His face from you,
So that He will not hear.
Habakkuk 1:13
You are of purer eyes than to behold evil,
And cannot look on wickedness.
So you see from just these two verses that God will not answer the prayer of a sinful person and will not even look at them. So how can we possibly ever be saved?
Jesus has reconciled us to God
Ephesians 2:13-16: But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. For He Himself is our peace, who has made both one, and has broken down the middle wall of separation, having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity.
2 Corinthians 2:19: ...God was in Christ reconciling the world to Himself...
Since Jesus has overcome the power of sin and even defeated death itself, He has redeemed the human condition unto God and endowed all of humanity with the free gift of salvation, the forgiveness of sins. But since you can't pray to God as a sinner, how are you to appropriate this gift of Christ's redemption of your humanity? FAITH. Faith operates in the human heart as the key to open the gift of Christ's finished work on the cross. Faith operates independently of and does not require God's positive intervention in order to do its work in us. Salvation has already been given to us. Faith is merely the act of accepting that gift; it is the key that opens the door to God's full pardon and blessing and adoption as His child, with all the benefits accorded to His Son Jesus.
Romans 10:6-10 But the righteousness of faith speaks in this way, "Do not say in your heart, 'Who will ascend into heaven?' " (that is, to bring Christ down from above) or, " 'Who will descend into the abyss?' " (that is, to bring Christ up from the dead). But what does it say? "The word is near you, in your mouth and in your heart" (that is, the word of faith which we preach): 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.