How do we know that believers are united in Christ?

The unity of believers in Christ is a mystery of faith, established before the foundation of the world when God chose His elect in Christ. Ephesians 1:4-5 highlights this eternal union, stating that God predestined us for adoption through Jesus Christ. This union is essential for our identity as children of God, fully realized in Galatians 3:28, which states that there is neither Jew nor Greek, slave nor free, male nor female; for we are all one in Christ Jesus. This theological foundation grounds our relationships with each other in the body of Christ.