Let Your “Is” Determine Your “Ought”

By Mark D. Roberts

June 24, 2019

Let no one deceive you with empty words, for because of such things God’s wrath comes on those who are disobedient. Therefore do not be partners with them. For you were once darkness, but now you are light in the Lord. Live as children of light.

Ephesians 5:6-8


As a philosophy major in college, I was required to take Phil 16: Introduction to Ethics. For a semester, my fellow students and I considered basic questions such as: What do we mean when we say actions are right or wrong? What is the nature of the good? Is morality rational? On what basis can we say that a person “ought” to do something?

snowy mountainPhilosophers have come up with a variety of answers to these questions. Some stress that the “ought” comes from figuring out the greatest good for the great number of people. Others argue that certain kinds of behavior have an essential “oughtness” independent from their results. You should keep your promise, these ethicists might say, no matter the results—because there is something inherently right about promise keeping.

Christian faith offers a variety of ethical approaches. Most obviously, we affirm that God determines what is right and wrong and that we ought to do whatever God commands. This is surely true. Yet it’s not the whole story.

In Ephesians 5:6-8, Christian ethics is not based on God’s commandments, but rather on our new identity in God. We are not to deceive or disobey. Why not? “For you were once darkness, but now you are light in the Lord. Live as children of light.” There is an “ought” here: You ought not to deceive or disobey. Instead, you ought to live as a child of the light. This “ought” is based on the “is” of your new identity: Now you are light in the Lord. If we want to find out what we “ought” to do (and not do), we need to pay attention to the “is” of our identity in Christ.

If this philosophical conversation seems a bit obscure to you, consider the following example. On April 14, 1984, while standing before family, friends, and God, I pledged myself in marriage. I became the husband of Linda. That wasn’t my entire identity, but being Linda’s husband became a central part of who I am as a person. Now, if I were tempted to be unfaithful to Linda and shared this temptation with a friend, he might very well say to me, “Mark, what are you thinking? You are a married man. You are Linda’s husband. Be who you are!”

Similarly, when you’re wondering how you should live your life, when you’re trying to figure out what’s right and why you should do it, remember this: Your “is” determines your “ought.” You are light in the Lord. So, be who you are. Live as a child of light!

Something to Think About:

Can you think of other examples, besides that of marriage, when the “is” of identity points to the “ought” of behavior?

To what extent does your identity as light determine your behavior?

How might you live as a child of light today?

Something to Do:

Do something today that expresses your identity as a child of the light.


Gracious God, thank you for giving me a new identity in you. Thank you for turning me from darkness to light. Thank you for making me a child of light.

Help me, Lord, to believe the truth about who I am in you. May the “ought” of my life be determined by the “is” of my new essence in you. Teach me to see myself as a light in you. By your grace may I live today and every day as a child of light. To you be all the glory. Amen.

Explore more at the Theology of Work Project:
Making Ethical Decisions in a Fallen World

Mark D. Roberts

Senior Strategist

Dr. Mark D. Roberts is a Senior Strategist for Fuller’s Max De Pree Center for Leadership, where he focuses on the spiritual development and thriving of leaders. He is the principal writer of the daily devotional, Life for Leaders,...

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