You never truly knew Him. You were never of Him. You never really surrendered to Hm or understood what it is to follow Him.
Okay that sort of mindset has always annoyed me to no end because it's not always true. Even the Bible suggests in some verses that you can walk away from being saved or you can lose your salvation, and it wasn't because you were never "of Him," it's because you decided that this wasn't the life you wanted. I'm glad that you've never had a moment where you've seriously questioned your faith, but guess what, it doesn't work that way for everyone. Even Job had a moment of doubt (and if anyone earned it he certainly did). Some people for whatever reason never question why they believe what they believe or if they made the right choice, they just assume they have and follow it almost blindly. My mom is one of these people. But for some of us life becomes too much or sometimes too much of Christianity just doesn't add up and it gets hard to follow something that in your mind does not make sense. It's better for her to follow beliefs that she herself has come to believe is true through experience, not just follow blind faith.