"’In Him’, don’t miss those two last, little, explosive, words. What this teaches is that because of our union with Him, because we are ‘in Him’, we become righteous [in] the same way Jesus became sinful. How did Jesus become sinful? Did He become sinful by sinning? No, nor do we become righteous by doing righteousness. He became sinful by having God recon to His account my sin, and I become righteous by having God recon to my account, His righteousness. And if that isn’t the best news in all the world, I don’t know what is because I know that in this life, both biblically and experientially, I’m not going to ever arrive at a point where I would qualify to be accepted by God. Ever! Therefore I must have the qualification from another, and it is His. And then the question is, ‘How do I get it?’ And the answer is ‘In Christ!’ United to Jesus, my sin is on Him, his righteousness is mine, and do you then see how huge this issue is? [Do you see] how important being ‘in Christ’ is? Union with Christ is not a throw-away, minor doctrine; it is at the center [of our doctrine]." - John Piper

(“United with Christ in Death and Life” by John Piper 10/8/2000. I personally transcribed and added the information in the brackets of this transcription.)