He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world. (NIV)

And He [that same Jesus Himself] is the propitiation (the atoning sacrifice) for our sins, and not for ours alone but also for [the sins of] the whole world. (AMP)

And he is the propitiation for our sins: and not for our's only, but also for the sins of the whole world. (KJV)