In the Bible, Jesus is called the Righteous One (Isaiah 53:11, Acts 13:14, 7:52, 22:14, 1 John 2:1).
This means Jesus was completely pure, clean, loving, holy...without a sinful thought, desire, or deed.
Everyone else is unrighteous (Romans 3:10).
Isaiah 53:11 revealed the Righteous One would come and make the unrighteous righteous by bearing their sinfulness and giving them his righteousness.
This is the Grace Exchange.
The Grace Exchange is when Jesus exchanged his righteousness for our sinfulness.