How do we know that the battle against sin is God's, not ours?

The battle against sin is ultimately not ours to fight by our efforts but belongs to God. This truth is captured in the promise found in 2 Chronicles 20, where God assures His people that they will not need to fight, for He will be their deliverance. Similarly, in the New Testament, we find that salvation was accomplished through Christ's sacrificial death—demonstrating that we do not earn our salvation through works or struggle (Ephesians 2:8-9). Instead, we are called to trust in Christ, the victor over sin, which affirms that the battle has already been fought and won by Him.