Yesterday's installment from Our Daily Bread makes a great point: God not only calls us to things; God also calls us away from things.
And the things that God calls us away from can be far more frightening than the things that God calls us to. After all, rightly and wrongly, we may derive security and even fulfillment from the things God calls us to leave behind.
But God wants us to rely only on Him for security, fulfillment, and life, and to thereby learn from the Author of life what it means to truly live. That's a hard thing to learn, something I seem to need to be retaught all the time. But it's a good thing to learn.