Leviticus 18:3 "You shall not do as they do in the land of Egypt, where you lived and you shall not do as they do in the land of Canaan to which I am bringing you."
The first reason for the insufficiency of Christ is having a wrong identity - thinking that you are your own, that the story is about you. The second is very related - engaging in the wrong story. We have already mentioned this but even if you believe that Christ is Savior and Lord, even if you think your identity is "Christian", if you have bought into the wrong story then, again, Christ will end up being insufficient for you. You may muddle through. You may just ignore your disappointment in Christ and His church or repress it but there will be a seed of bitterness and sadness and even anger at God that makes a home in your heart and turns your yearning for Him into questions and wonderings and mistrustings and giving up-ings.
The STORY: There are two movements in the Exodus story: leaving and entering. God says that His people can no longer live the story of slaves in Egypt. Most people, even non-Christians, get this. Everyone wants to leave the past and embrace the freedom to be themselves. But usually they are too afraid and if they try they typically make a mess of leaving. Therapists are therefore making a fortune... on Bandaids. The great tragedy in this is that some people actually do leave but are not able to complete the process by entering Canaan. They end up back as slaves in Egypt with the added problem of now thinking that leaving doesn't work. Back as slaves and mad at God for not coming through, not showing up, not being big enough, not making life work. They chalk up Christianity as one more philosophy/religion that is really nice, makes sense of some things and provides some comfort while they make more bricks for Pharaoh.
Even if we believe that we belong to Christ, even if we serve Him in some way or another, our joy and peace and power and perseverance will be ever just out of reach if we are not in Canaan living His story.
Some would say that Jesus as Savior is enough but we are not free by being set free from Egypt, as essential as that is. If we do not accept freedom, respond to freedom and follow God to the Promised Land, we may not be slaves to Pharaoh but we remain slaves to wandererings in the desert. Of course, neither leaving nor entering is accomplished by our own hands. God must part the Red Sea and the Jordan as well. He saves us time and again but without our response to His Lordship in Canaan, His Saviorship at the Red Sea is a despised, unwrapped and useless gift. The story is within Christ as Savior and Lord.