The Hebrew word yare'ach refers to the moon as a celestial body. It is one of two primary Hebrew terms for the moon (cf. levanah, H3842). The word may relate to the root for wandering or to light. The moon was a central marker in Israel's calendar system, governing the new month (rosh chodesh) and festival timing.
God created the moon as the lesser light to govern the night and mark sacred times (Genesis 1:16; Psalm 104:19). Israel's lunar calendar meant the moon was intrinsic to Sabbath, Passover, and all major feasts. The moon reflects the sun's light — a theological picture of believers reflecting God's glory. Eschatologically, the moon turning to blood (Joel 2:31; Revelation 6:12) marks cataclysmic judgment. In the New Jerusalem there is no need for moon or sun, for God Himself is the light (Revelation 21:23).