IMO the problem comes with watering down Christ's lordship. He's more than our Savior - we need to make Him our King in all our affairs, not just missions.
I agree, in that, if Jesus IS truly God in the flesh, if He truly sacrificially died on the cruel cross to save us, if He truly is Lord over all, then believing on Him and receiving His gift of eternal life through faith, we can't help but go all the way and surrender everything to His will. BUT...this full understanding comes over time, it is learned and is a part of a mature faith. Just as God tests our faith to strengthen and refine it, so we learn that God IS trustWORTHY.
There is NO chance at all that I will EVER reject my faith in Christ - I've seen too much, experienced too much, to ever go back to entertaining doubts. As new believers sometimes do - and it is NOT a shameful thing to acknowledge - we have to grow in grace and in the knowledge of Jesus Christ. It is when we see over and over how God provides, how He is there even in our darkest hours, how he never will leave us or forsake us, that we reach maturity in the faith. This is the kind of faith that moves mountains, that is willing to do whatever the Master commands, because God is faithful and works ALL things for our good and we KNOW it.