"God tests his people by actual experience. He did not test Abraham by words only; he did not say to him, "Will you do this? Are you willing to do that?" It is always easy to say that we will do a thing if we do not expect to be compelled to do it. We can make large promises when we think we shall never be called upon to fulfill them; we can even think large things today about what we intend to do tomorrow. It is always easy to rise up early overnight. But God does not prove his people in word only, but in deed and in truth."
--Spurgeon, excerpted from Abraham's Trial: A Lesson For Believers