Only righteous Jesus can and did, once and for all, transform the evilest day of our making into the Good Friday of His own accomplishment; not by avoiding our evil, but by swallowing our evil so entirely and so undeservedly that God's holy wrath was completely satisfied, thus opening the one and only way for our reconciliation with God through Himself. "For our sake He made Him to be sin who knew no sin, so that in Him we might become the righteousness of God" (2 Corinthians 5:21). Hallelujah, what a Savior!
For this reason the Apostle Paul, and billions since him (including me) who find in his sentence the heart of God so beautifully expressed, makes this plea: "Therefore, we are ambassadors for Christ, God making His appeal through us. We implore you on behalf of Christ, be reconciled to God" (2 Corinthians 5:20).
Ever since the Fall, when Adam and Eve "held open the door" for sin, guilt, and death to enter into the world, we have been trying to cover our shame with our own schemes and shams. Whether it was our first primitive coverings sewn of fig leaves or our most modern tapestries woven of eclectic threads of philosophy, our own attempts to contain or control or conceal our sin by non-gospel means have accomplished neither concealment nor control nor containment. In fact, our best efforts to erase our sin have only increased our sin by adding self-righteousness and disbelief to our failures, further accelerating our destruction and further complicating our enmity with God. Without Christ we are utterly trapped, totally lost, and unavoidably dead in our sins.
But Christ, who knew no sin, came to cover our sin entirely with Himself. Foreshadowed by the animal skins that God provided our great-grandparents on the day of their spiritual death, which temporarily covered their shame, the true and perpetual covering of sin came in Christ's sacrifice. His blood covered our sin in two important ways: it completely removed the stain of our guilt (expiation) and it completely endured the fierce judgment of our God thus yielding to grounds for friendship with the Holy (propitiation).
Theologians rightly refer to a double imputation. (1) Our sin was mercifully imputed to Christ, where He suffered the full and necessary wrath of God in our place. Also, (2) His righteousness was graciously imputed to us, where God can now have full fellowship with us through His Son's resurrection victory. Both imputations are essential or else God's justice and Christ's mercy would never meet and convert the sinner.
The salvation-life can be summarized in terms of covering--putting off the clothes of the old man (e.g. repenting of both our sin and our "fig leaves") and putting on the righteous garment of Christ (e.g. believing in the exclusive offer of Christ's character as our final covering accessible only by faith).