Isaiah 40:18 asks: “To whom can you liken El? What likeness can you compare him to?” (Similar questions are posed in Isaiah 40:25 and 46:5.) The questions are rhetorical. The prophet’s point is that God is incomparable. As the verses following Isaiah 40:18 explain, it is absurd to make an image of God. Many Old Testament passages echo these sentiments (see Exodus 8:10; 15:11; Deuteronomy 33:26; 1 Samuel 2:2; 2 Samuel 7:22; 1 Kings 8:23; Micah 7:18; Psalm 89:7 [6 in English]; 1 Chronicles 17:20).
But if there is nothing to which God can be compared, how can a person know anything about Him or worship Him? Even the poet who penned these verses compared God’s attributed to what his readers could conceive and understand: “He will feed his flock like a shepherd” (Isaiah 40:11).