How does a believer know they are chosen by God?

Assurance of election comes through faith in Christ as revealed in the gospel. Paul stated in 1 Thessalonians 1:5, "For our gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance." The genuine experience of faith, the conviction of the Holy Spirit, and the fruits of that faith provide the evidence of being chosen. Assurance should rest not on personal feelings but on the promises of Christ and what He has accomplished through His death and resurrection.