Christ's death is not just a substitute for our death, His life is a substitute for our lives. Christ's obedience to the Father becomes our obedience to the Father; Christ's trust in the Father becomes our trust in the Father; Christ's yieldedness to the Holy Spirit becomes our yieldedness to the Holy Spirit. When I claim Christ as my substitute life it leads to such security and it so takes the performance pressure off in which we are at such peace that we can cultivate a desire for holiness.