How do we know that Jesus died for His people?

In Matthew 1:21, the angel proclaims to Joseph that Mary will bear a son, and He will save His people from their sins. This explicit declaration underscores the particularity of Christ's atoning work — He did not come merely to offer salvation, but to effectively save His people. Furthermore, in Acts 20:28, Paul reminds us that Christ purchased the church with His own blood, reinforcing that His sacrifice was not for the sins of all humanity, but for the specific group known as His people. This guarantee of salvation for those given to Him reveals God's design and purpose in the atonement.