What does 'He laid down His life for His sheep' mean?

The phrase 'He laid down His life for His sheep' (John 10:15) encapsulates the doctrine of substitutionary atonement, central to Reformed theology. This doctrine teaches that Jesus died specifically for those whom the Father had given Him, ensuring their salvation. His death is portrayed as a sacrificial offering, where He takes upon Himself the sins of His people. This underscores God’s sovereignty in salvation, demonstrating that Christ's atonement was not a general act but a targeted, effective sacrifice that secures eternal redemption for the elect, satisfying justice once for all.