OK so I think I need some assistance here for the future when this topic comes up again.
I got into a discussion with a Jehovah's witness who clearly loves the Lord, but does not believe that once a person is saved, that they are always saved. I explained to this person that if you truly, truly are converted then you know you are saved. I explained the passage in John chapter 3 where Christ was talking to Nicodemus that you have to be born again. I also explained the difference between a person who thinks they are saved and those who really are saved and my personal experience. I mentioned the Bible verse where God says that "no one can pluck My children out of My hand" and I went on to say that if one could lose their salvation, then Christ's death and resurrection was not perfect, therefore He would not be the Messiah and we would be continually sacrificing like in the Old Testament. This person kept arguing with me that if you are saved and you commit a big sin, or if Christ returned and you are not doing what you are supposed to do, then you won't be saved. Then this person said that if you are not saved, then you are just no more, meaning your soul does not exist. I explained that our soul never dies, we are either in eternity with God forever or separated from Him in eternal damnation.
I feel frustrated that I did not have enough supporting scriptures on this.