It helps if you start at the beginning of the chapter.
It is a logical progression showing that we are not under the law, but rather under the new covenant of Jesus Christ’s sacrifice... However, he also shows in this argument that born again christians should not use this as an excuse to sin, because it can still lead to our physical death.
Just because we have Christ does not free us from the law unto our flesh... but it does free us from the “Law of sin and death” which directly governs our life after death.
Someone who has received Jesus as their savior cannot revoke their salvation by sinning... but they are not freed from the immediate consequences of sin, which brings judgment to the flesh.