The Hebrew verb arab (עָרַב) has two meanings: (1) to grow dark, become evening, and (2) to be sweet, pleasant, or agreeable. The related noun erev (H6153) means evening — the liminal time between day and night.
The Hebrew day began at evening — "and there was evening and there was morning, the first day" (Genesis 1:5). Darkness is not an enemy but a beginning. The sweetness sense appears in Psalm 104:34: "My meditation of him shall be sweet." The transition of evening — like the sweetness of rest — becomes a figure for contemplative intimacy with God.