Rom 5:11
11 And not only so, but we also joy in God through our Lord Jesus Christ, by whom we have now received the atonement.
The Atonement of Christ has reconciled the elect world to God. It secured and ensured for it [ the elect world] every spiritual blessing needed to live unto God and for His Glory through Jesus christ.
Even before the elect are born into this world as sinners, they have already [by the blood of Christ] been reconciled to God, it will now be a matter of time for it to be manifested.
The atonement accomplished the complete salvation for all whom it was offered for, that is the death of christ. It provides them Faith, repentance, sanctification, redemption, and every needful spiritual blessing to convert them to God, and remain secured forever.
In principle, you are correct that God chose the elect to be saved before he made anything and anyone, but in practice, he enables us to believe in and follow Jesus. I think that this distinction between principle and practice would help you understand the Bible's teachings. The Bible fully shares with us two mysterious threads of thought. First, God has his plan for all believers long before we are alive. Second, we are completely responsible for all our thoughts, words, and actions. Both are true, though mysterious (Genesis 50:20).