When Paul wrote in Romans 8:30 that those whom God calls, He also justifies, he did not say that those whom God calls are justified, if they should cooperate by making the right decision. Paul said without ambiguity
and without any added conditions whatsoever that those whom God calls He also justifies. Any added implication of the decision of man being necessary is something that is not contained in the Scripture.
No one resists this inward, effectual calling of God. Many may reject the outward call of the spoken or written Gospel message, but all of those who are called inwardly by God do indeed come to faith in Christ, and none who receive this calling resist it or refuse it. This is the destiny of those of us whom God has chosen to come to faith in His Son Jesus Christ, and it is a destiny that God decided and appointed for us before the world was created.
The Apostle Peter also spoke of God’s elect, or those chosen by God, when he addressed the recipients of his first letter with the words: “To those who reside as aliens, scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia, who are chosen according to the foreknowledge of God the Father, by the sanctifying work of the Spirit, to obey Jesus Christ and be sprinkled with His blood: May grace and peace be yours in the fullest measure” (1 Peter 1:1-2).
Peter addressed his epistle to those who are “chosen according to the foreknowledge of God the Father”, as Paul also taught in Romans 8:29-30. For what purpose were they chosen? They were chosen by God “to obey Jesus Christ and be sprinkled with His blood”. And God’s choice of His elect was made before the foundation of the world (Ephesians 1:4-5).