What does the term “heaped high as heaven” mean?

This phrase awakens in the eyes of our minds an enormously high pile (of sin). In fact, the picture required by the Greek words used here (literally, “her sins have clung even to heaven”) is of sin glued to heaven. The verb John uses is the same as appears in Luke 10:11 to describe what road dust does to one’s feet (clings; see also Romans 12:9; 1 Corinthians 6:16). Babylon’s sins have, in a manner of speaking, been thrown into the face of God in heaven, and they stick, as it were, to heaven as glue-laden leaves to a ceiling. In the face of that arrogant audacity, God in heaven must respond with his plagues.