What defines a true Christian?

1 Peter 1:8-9
“8 Though you have not seen him, you love him; and even though you do not see him now, you believe in him and are filled with an inexpressible and glorious joy, 9 for you are receiving the end result of your faith, the salvation of your souls.”
What defines a true Christian more than anything else? It is love for Christ! Love that is demonstrated by obedience. You can have all the doctrines right and not be saved. You can have an emotional attachment, call it love, but if you life is not marked by obedience to the Word of God your love is a lie. Any woman knows that her husband doesn’t really love her if he’s playing around with another woman on the side. It doesn’t matter what he says. True love for Christ obeys joyfully, mourns at every failure and turns away from disobedience.
1 John 5:3 (NIV) In fact, this is love for God: to keep his commands. And his commands are not burdensome,
Here is a quote from John MacArthur:
 “’Though you have not seen him, you love him.’ Though you have not seen him, you love him.  That’s the bottom line.  We have a love for Jesus Christ.  “If anybody doesn’t love the Lord Jesus Christ – ” 1 Corinthians 16:22 “ – let him be accursed.”  This is a profound statement about the nature of true salvation.  It is characterized not only by faith in Christ, believing in him, but loving him. 
“You heard somebody in baptism say, “Just because I believed the facts I assumed I was a Christian.”  You can believe the facts and not be saved.  The devil believes the facts.  The demons believe the facts.  They know them to be true.  The issue here is loving the Lord Jesus Christ.  “And you love me if you keep my – ” what? “ – my commandments.  You love me if you desire my glory and my honor.”  Though you have not seen him, you love him.
“If you were to define Christianity in its purest sense, you would have to use that word ‘love.’  You could talk about believing in Christ, but you really wouldn’t get there because so many people say they believe in Jesus Christ.  In fact, I read a foolish article today in which a man said there are three billion Christians in the world.  Well there are probably three billion people who believe in Jesus, but I’m quite sure there aren’t that many who love him, who love him sacrificially, who love him totally, who love him obediently, who love him worshipfully, who love him righteously.  ‘And because we love him, though we do not see him now – ‘ verse 8 says, ‘ – but believe in him, you greatly rejoice with joy inexpressible and full of glory.’
“And he knows if we love him.  1 John 4:19 says, “We love him because he first loved us.”  You know a true human relationship requires love and trust.  Love and trust.  So does our relationship with Christ.  That’s how it’s really defined.  And there’s no such thing as a Christian who doesn’t love Christ.  In all your life long as a believer you grow in your love for Christ.  You grow in your affection for him.”