You see, the death Jesus died on the cross was our eternal damnation. What He endured on the cross was our Final Judgment! When Paul says, "There is therefore now no condemnation for those who are in Christ Jesus," he was in effect saying, "There is therefore now no Final Judgment for those who are in Christ Jesus." Your Final Judgment is not in the future; it is in the past, in the death of Jesus Christ if you believe in Him! When "the clouds be rolled as a scroll, the trump shall resound and the Lord shall descend…"; when those who rejected Christ call out to the mountains and rocks, "Fall on us and hide us from the face of him who is seated on the throne, and from the wrath of the Lamb" (Rev. 6:16), we will be able to sing with wonder and transport, "It is well with my soul!" How is that possible? "My sin--oh, the bliss of this glorious thought!--my sin, not in part but the whole, is nailed to the cross and I bear it no more!"
Justification is an act of God's grace. If you believe in Jesus Christ, it's done, eternally done, once and for all. And the faith by which you receive this eschatological justification is extra-spective in nature: it looks away from ourselves--from our helplessness to live perfectly as God demands, from our hopelessness to earn our salvation, from our repeatedly failures and sins (even seventy times seven in a day!), from our disappointment in ourselves and even our disgust with ourselves--toward Christ who has done all things well! So, don't forget this when you fail again--look to Christ who is your justification and salvation! Don't forget this when you fall and make sure you fall into the nail-pierced hands of Jesus Christ!