and He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed. [1 Peter 2:24]
When Isaiah wrote that (see Isaiah 53:5), it was a prophecy of what Christ would go through. When Peter wrote that, it was to remind the readers, and us, that Christ had fulfilled that prophecy, and the suffering He went through: stripes, wounds, and death on that cruel cross. Peter explained that it was for us that Christ went through that. He took our place and bore our sins, so that we, being dead to sin, can live for what is right.