If you love Me, you will keep My commandments. (John 14:15)
One of the definitive evidences that someone is really a Christian and not just a false professor, is their love for Jesus Christ. Jesus said, "If you love Me, you will keep My commandments." Those who profess to be Christians and love the Lord but don't obey His word are deceived false converts still lost in their sins; But prove yourselves doers of the word, and not merely hearers who delude themselves. (James 1:22)
Of course, no one is saved and becomes a Christian by their obedience alone. Salvation comes by the grace of God through faith alone in the finished work of Christ alone; For we maintain that a man is justified by faith apart from the works of the law. (Romans 3:28) However; Even so faith, if it has no works, is dead, being by itself. (James 2:17)
I recently had a brief conversation with a nice young man who said he was a Christian. I told him that I was a Pastor and asked him about his Christian conversion. He said that he had trusted Christ as his Lord and Savior several years ago, although he no longer was part of a local church and didn't know much about the bible. He also told me that he was "moving-in" with his girlfriend. When I pointed out what the bible says about their premarital relationship, he acknowledged that God probably wouldn't approve, but that for "practical" reasons they have decided living together before marriage is best.
This young man's practical logic and world view is acceptable and common in our modern culture but belies his Christian profession. If I get another opportunity, I will go over the gospel with him again because I doubt that he is a Christian and that really loves the Lord; So, faith comes from hearing, and hearing by the word of Christ. (Romans 10:17) Maranatha!