I grew up attending a church of Christ church. I had heard many sermons that seemed to imply that you could lose your salvation. I was horribly conflicted throughout college, and wrote down quite a few scriptures in my prayer journal that convinced me that my salvation could not be lost. But I was never able to fully understand or reconcile in my mind what the Bible meant when it talked about falling from grace.
And then in church last Sunday, our pastor made an amazing analogy that felt like God gently thumped me on the forehead and said, "There ya go! Get it now?" In a kind and loving way, of course! The really amusing thing to me is that B had the same realization at exactly the same moment I did. We just looked at each other and went, "OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOH!" As in, we get it now!
So the analogy was this (Forgive me, PG, if I slaughter the story!)...imagine you are riding on a 767 jet airplane. The plane takes off and climbs until it reaches its cruising altitude of 37,000 feet. And at that moment you decide that you can fly the rest of the journey to your destination on your own, so you open the door to the airplane and jump out.
Do you fly safely to your journey? NO! You fall like a sack of rocks straight to the earth.
Falling from grace is when we stop looking to God for everything, and start looking to ourselves for our salvation. If I'm just GOOD enough, I'll get to heaven. We aren't living by the grace of God any longer, we are trying to live by good works. And if you believe that the Bible is the inerrant and infallible word of God, you know that you cannot save yourself just by being a good person. We can't save ourselves, we needed a saviour and that is why Jesus came to the earth. Salvation is a gift that we simply accept. Yes, it is THAT easy! We admit we are sinners in need of a saviour, and we accept the gift of life that Jesus provides through his death on the cross and resurrection three days later. And then we spend the rest of our lives trying (and failing, and trying again and failing again because we are fallen, imperfect beings, hence the need for a saviour in the first place!) to live according to how God wants us to live, because we greatly appreciate the gift of eternal life He has given us and we want to be pleasing to Him.