It is upon the rock of our Redeemer, who is Christ, the Son of God, ... whereon if men build they cannot fall. Helaman 5:12

And now, my sons, remember, remember that it is upon the rock of our Redeemer, who is Christ , the son of God, that ye must build your foundation; that when the devil shall shall send forth his mighty winds, his shafts in the mighty whirlwind, yea when all his hail and his mighty storms shall beat upon you, it shall  have no power over you to drag you down to the gulf of misery and endless wo, because of the rock upon which you are built, which is is a sure foundation whereon if men build they cannot fall. Helaman 5:12. So I guess what that mean is that if we fall, we fall because we slipped off that rock.