This week in I Thessalonians 1 we're going to hear the apostle Paul glory in God's sovereign, electing grace, which gave him assurance the the Thessalonians' faith was real and would persevere. Many people have a hard time with the Bible's teaching that Christ only died for some and not for every single person in history. Though election challenges our modern notions of fairness, it is necessary for upholding God's justice.
The great Puritan John Owen explains it this way: If Christ died for all on the Cross (if He actually paid for their sins), but not all are finally saved, then those unbelievers who suffer God's condemnation at the final Judgment suffer unjustly, since they receive from God a second payment for their sins (the first having been paid by Christ on the Cross). The only way out of this scenario of unjust, double jeopardy is the biblical doctrine of particular atonement, that Christ actually died for some (the elect) and because the sins of the elect have been fully paid by Christ on the Cross, no future condemnation for them is possible.