Heidelberg Q. 94. What does the LORD require in the first commandment?
A. That for the sake of my very salvation I avoid and flee all idolatry, witchcraft, superstition, and prayer to saints or to other creatures. Further, that I rightly come to know the only true God, trust in Him alone, submit to Him with all humility and patience, expect all good from Him only, and love, fear, and honor Him with all my heart. In short, that I forsake all creatures rather than do the least thing against His will.

Heidelberg Q. 95. What is idolatry?
A. Idolatry is having or inventing something in which to put our trust instead of, or in addition to, the only true God who has revealed Himself in His Word.