Ponder these words from Martin Luther, quoted in Sunday’s sermon:

This is . . . establishing idolatry: undertaking to worship God without God’s bidding, on the basis of one’s own devout inclinations. For he will not have us direct him how he is to be served. He intends to teach and direct us in this matter. His Word is to be there. This is to give us light and guidance. Without his Word all is idolatry and lies, however devout it may seem and however beautiful it may appear. . . .

For here you learn that it is not enough to say and think: “I am doing this for the glory of God; I intend it for the true God; I want to serve the only God.” All idolaters say and intend just that.

(As quoted in Michael Horton, The Law of Perfect Freedom: Relating to God and Others Through the Ten Commandments (Moody, 1993), p. 83-84.  The original source is Luther’s 1532 Preface to the Prophets, which is available online at this link, although in a different translation. The section on idolatry begins at about the halfway point with the phrase  “since the prophets cry out most of all against idolatry.” This quote begins with the phrase, “That is the real committing of idolatry.”)