'ARAV
This Hebrew word is not only a fascinating study, but is loaded with insightful meaning. This root word literally means to "mix a substance", or to "penetrate with foreign matter". This word is used to express "mingling" or "mixing", as in Mizmor 106:35. "But were mingled among the nations and learned their works." One of the major cognates of this word is 'erev. This is the word for "evening". Evening begins the day in scripture. The evening begins as a mixture of light and darkness. When the children of Israel came out of Egypt in Sh'mot 12:38, they came out as a "'erev rav", or a "mixed multitude", yet all were referred to as the children of Israel. YHVH hates a mix, so this is why He always makes two things one. A goy cannot enter the congregation of Israel and remain a goy. This is a mix. One day there will be no more evening, no more mixing.
Z'kharyah 14:7
"But it shall be one day which shall be known to YHVH, not day, nor night; but it shall come to pass that at evening time, it shall be LIGHT."
Shalom Alecheim!