If God required the death of His Son, the Lord Jesus Christ, then salvation by any other means is impossible. Christ's death is an unassailable argument against salvation by all contributions from man.
God's justice required the death of His Son to save His people from their sins. God gave His Son to die for His people for no cause in them; it was by grace alone. Christ's death was satisfaction to God's justice. It was an act of His pure, free grace. Salvation is therefore according to justice, by grace alone.
Anything from man is necessarily excluded in salvation. If God’s justice required the death of His Son, then surely no other way is possible. Would God take pleasure in the death of His Son if His Son did not need to die?! If God, in grace, gave His Son to die, then surely nothing from man could earn salvation. Can man earn the death of the Son of God?!
All have sinned, and there is none righteous. Therefore, salvation by man’s personal obedience is impossible. But nothing makes it more impossible than for God to require His Son’s death, and for Christ to give Himself to death, for nothing.
To save His people from their sins, God the Son humbled Himself as a servant, took the nature of His people as His own, was made under the law, made sin for them, and offered Himself in obedience to the will of God by His death on the cross, in satisfaction to God's justice. By His one offering, Christ perfected His people forever, establishing their everlasting righteousness.
Therefore nothing involving us makes us acceptable to God: nothing done by us and nothing done in us. All that includes man is excluded. God’s people were made righteous entirely outside of their own personal experience. Christ's death finished the work of our salvation.
Is Christ everything in your salvation? Then God has given everything to you. But if you need something in addition to Christ, then Christ is nothing to you, and you are nothing to God.
Mark 14:36; Acts 17:3; Hebrews 2:10; Isaiah 53:10; Revelation 13:8; Romans 4:25
2 Corinthians 5:21
Romans 3:21-28; Hebrews 10:5-14
1 Corinthians 1:30; Daniel 9:24
Isaiah 45:24; Jeremiah 23:6; 33:16
John 17:4; John 19:28-30