1 Peter 1:1-2 NASB:
‘Peter, an apostle of Jesus Christ, to those who reside as aliens, scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia, who are chosen according to the foreknowledge of God 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.”
Peter uses covenant language, pointing to Mount Sinai and Exodus 24, but clarifies that the covenant in view is the New Covenant in the blood of Christ. Peter is Christ’s apostle and refers to himself with the name given him by Jesus.
Next we encounter phrases, which modify or describe how his audience became chosen aliens. First it was according to the foreknowledge of God – God’s redemption plan was to choose believers for His own possession. Second they became chosen aliens by the sanctifying work of the Spirit. Here “sanctifying work” refers to God setting the person apart – spiritually in Christ – rather than the process of sanctification that occurs once a person is placed spiritually in Christ. And third, we have the phrase “to obey Jesus Christ and be sprinkled with His blood.
In summary, the encouragement provided by Peter’s first letter is based on the readers understanding that they are aliens suffering difficulty in the world because they were chosen out of the world and made citizens of the kingdom through the New Covenant in His blood.
Since 1 Peter 1:1-2 uses "by the sanctifying work of the Spirit to describe how the chosen aliens came to their present situation, without any "for salvation" to be found, it is clear that "by the sanctifying work of the Spirit" and "through the sanctification by the Spirit" (2 Thessalonians 2:13) both refer to God setting individuals apart in Christ as the means of being chosen, not saved.
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