Christ's Atoning Death !
You see sin resulted in alienation and hostility in our minds as is pointed out here Col 1:21
21And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled
Let me say something here. This verse is not only describing the fornicators, drunkards, drug attics in the world, but also the very religious people, the very moral people, people who live decently and honestly before men, but they just don't have the True Christ.
Also Eph 2:1-3
1 And you hath he quickened, who were dead in trespasses and sins;
2 Wherein in time past ye walked according to the course of this world, according to the prince of the power of the air, the spirit that now worketh in the children of disobedience:
3 Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.
Notice Paul said that he also walked in the lusts of the flesh, fulfilling the desires of the flesh and the mind, now paul I do not believe was a fornicator, a thief or a drunkard, but this is what characterized previous lifestyle Phil 3:4-6
4 Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more:
5 Circumcised the eighth day, of the stock of Israel, of the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee;
6 Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless.
Paul was I believe a very pious and religious man, perhaps from his youth.
But when he was saved, he looks back at that lifestyle just described in Phil 3 as one of being "fulfilling the desires of the flesh and the mind".
Eph 4:17-18
17This I say therefore, and testify in the Lord, that ye henceforth walk not as other Gentiles walk, in the vanity of their mind,
18 Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:
However, the reconciliation and atoning benefits of Christ's death, the Holy Spirit working in conjunction with it, working in them that Christ died for, works so in them to present them Holy and Blameless before God, in the Day of Christ. Col 1:21-22
21And you, that were sometime alienated and enemies in your mind by wicked works, yet now hath he reconciled
22In the body of his flesh through death, to present you holy and unblameable and unreproveable in his sight:
Phil 1:6
6 Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ:
So the commencing of the good work in us , reconciling us to God subjectively, is what Paul means by us receiving the Atonement, we have received of its mighty effects, it begins a work in us by God the Holy Spirit, that actively brings back to God, Thats the Atonement that Christ's provides for everyone he died for, God's Elect. 73