Jesus is arrested and faces an illegal trial where He is rejected, not because He is lying, but because what He has said openly for years is offensive to the ears of sinners. Jesus boldly proclaims the truth.
While this is happening, His disciple Peter denies the truth about knowing Him and belonging to Him - three times.
The prophecy of God would be fulfilled: all people (including Peter) would need to be saved by one man.
Christ did not die to save us in response to His disciples' confession of Him. Rather it would be Christ's death that would sustain the faith and confession all of those who belong to Him.
Jesus' sacrifice was not dependant on the faithfulness of His people. Rather, the boldness and faithfulness of the people whom He would save by His death would be dependant on His sacrifice.