Protestants don’t believe the atonement removed all sin. Instead, Jesus’ sacrifice removed the penalty of sin - that’s a big difference.
Christians have 2 natures. As Paul points out when one is born again, they are filled with the Holy Spirit, but the “old man” or flesh nature is still present in the believer at war with the Holy Spirit. Everyone still sins because we still have the flesh nature within us, which will remain until we get to Heaven.
So we are still in our sin... just not liable for penalty? What of the "regenerated" Christian who commits murder (and please don't deny that there have been some in history)?
Christians have 2 natures. As Paul points out when one is born again, they are filled with the Holy Spirit, but the “old man” or flesh nature is still present in the believer at war with the Holy Spirit. Everyone still sins because we still have the flesh nature within us, which will remain until we get to Heaven.
And what if we give in to the "flesh nature"...?