Beloved of God. 1st Thessalonians 1:4 “Knowing” in this verse is based on observation, not intuition or revelation. That knowledge came when Paul personally saw (v.5-10) evidence consistent with those whom God has chosen to represent Him and be with Him. A spiritual “brotherhood” includes Jewish and Gentile brothers and sisters in Christ. God’s choice is based on their response to the Lord Jesus Christ by placing personal faith in Him. Sixteen times in 1st Thessalonians, Paul uses the word “brethren” to identify those whom God had called in that place through His sovereign electing love.
God’s love is unconditionally extended without expecting undeserving sinners to return their love to Him. “God so loved the world, that He gave His only begotten Son…” When a person accepts the Lord Jesus Christ as their personal Savior, they will eventually realize they have been “Chosen not for good in me, wakened up from wrath to flee,” but were designated as those who gladly “received Him.” That election concerns the position and privileges we have as believers.
“Brethren beloved,” or perhaps better, “brethren beloved by God,” are believers whom the Lord loves unconditionally. They are part of the same family as Paul, sharing the same interests and thoughts as others in God's family. They have experienced election not through their own intuition but by God’s grace. They recognize its blessings by observing the difference in the lives of believers compared to those of the world. The elect are beloved by God and chosen by God, even if we cannot fully explain it. Our knowledge of this is genuine because of what we see and hear. By faith, we recognize that God demonstrated His love for us while we were sinners, and it is a fact that “Christ died for us.”