In Luke 4:4, Jesus tells the Devil, in response to the first of his temptations, "It is written: 'Man shall not live by bread alone, but by every word of God.'" This is not some general statement that allows us to choose what we will and will not obey, but a requirement for each of us, to the best of our ability, to follow every word of God in living our lives before Him. To do this takes real faith. God has given us "the way of righteousness," a revelation this world just cannot comprehend, and He is looking for evidence that we not only assent to it but are also living it.
It is the works of obedience that change us, that reflect that we are striving to live as God lives. This is what God counts as proper evidence of our faith. In James 2:17, 20, 26, the apostle informs us that, without works, our faith is dead, and these works are defined as putting into practice the instructions of God in our lives, just as Abraham did on Mount Moriah (Genesis 22:2-12).
When God saw Abraham's obedience to His instructions, He said, "Now I know that you fear Me!" As hard as it is for us to measure up to what Abraham did in being willing to sacrifice his only son in obedience to God's command, God should be able to say this about each one of us. Do we have the faith to live by every word of God?
Humbling ourselves in obedience—especially when it hurts—makes a powerful statement to God.