How do we know that believers will not receive wrath?
Answered in 1 source
Believers' assurance is rooted in the gospel that states they are appointed to obtain salvation through Jesus Christ, who died for them.
Paul assures believers in 1 Thessalonians 5:9 that God has not appointed His people to wrath but to obtain salvation through the Lord Jesus Christ. This comfort is based upon the completed work of Christ, who bore the wrath of God on behalf of His people. The certainty of salvation for the elect is anchored in the faith that Christ's atonement was sufficient and effective. It is this gospel promise, that whether awake or asleep, believers shall live together with Him, that fortifies their hope and reassures them of their standing before God. This divine promise reflects the sovereign grace that characterizes the Reformed understanding of salvation.
Commentary