2 Corinthians 5:21
For our sake [God] made him who knew no sin to become sin, so that, in Him, we might become the righteousness of God
We are sinners and Jesus is not. Sin is not breaking arbitrary commands which aren’t that important. It’s rebellion, treason, adultery. We have tried to put ourselves in God’s place, to be in authority over ourselves. All of that sin, that rebellion, that betrayal was taken by Jesus on the cross. He became our sin. He took our punishment. He didn’t rebel, but was treated as if he did, so that rebels like us can be treated as if we didn’t.
For our sake [God] made him who knew no sin to become sin, so that, in Him, we might become the righteousness of God
We are sinners and Jesus is not. Sin is not breaking arbitrary commands which aren’t that important. It’s rebellion, treason, adultery. We have tried to put ourselves in God’s place, to be in authority over ourselves. All of that sin, that rebellion, that betrayal was taken by Jesus on the cross. He became our sin. He took our punishment. He didn’t rebel, but was treated as if he did, so that rebels like us can be treated as if we didn’t.
That’s part of the story. But we don’t just have our sin taken away, Jesus gives us his righteousness. So it’s not just as if we haven’t sinned, but God treats us as if we have perfectly obeyed. That is how gracious He is! We are embraced by God because Jesus took our sin and gave us his righteousness.
Sometimes we accept this at conversion and then start living as if now we have to maintain our own righteousness. The reality is that we are just as incapable of maintaining our own righteousness as we were of achieving it in the first place. Whether you’ve been a Christian 30 seconds or 30 years, you stand before God because Jesus took your sin and gave you his righteousness.
Imagine a day when everything went well: you woke up before the alarm and even though your bible reading plan was in Leviticus, the words seemed to jump off the page and warm your heart. You prayed with great faith, got into work early and were able to help others with their work after completing your own. At lunch time someone said "I've noticed something different about the way you live your life... can you tell me more about Christianity?" and you were able to share the gospel and invite them to church. You went home, spent time with your wife and kids and felt great as you sat down to pray before bed.
Then imagine the opposite: You wake up late and have to skip your quiet time. You get stuck in traffic and everything goes wrong at work, leading you to speak harshly to some of your colleagues. You get in an argument with someone at lunchtime about a TV programme that said the bible couldn't be trusted, and a friend who you'd previously invited to church witnesses the argument and changes their mind about coming along this Sunday. You get home late, argue with your wife, shout at your kids, and feel terrible as you sit down to pray before bed.
We feel like we can come before God with our heads held high on the good day, and that we need to sort ourselves out a bit on the bad day. We think the good day is good and the bad day is bad, but, ion fact, they’re both bad if we are using them as the basis for our relationship with God. The only reason we can stand before God on either of those days is because Jesus took our sin and gave us His righteousness. There's nothing wrong with getting excited about what God has done on the good day, and it's likely that there will be consequences of the mistakes we made on the "bad" day BUT we are totally dependant on Jesus performance, not ours, in terms of righteousness before God. It's not about what you do, but about what He has done.