Hi,

Just a little more information that might shed some light on this passage:

     "Yet another name for Rosh HaShanah is Yom HaKeseh, "The Day of the 
     Hiding" or "the Hidden Day." The term keseh or keceh is derived from 
     the Hebrew root kacah, which means to "conceal, cover, or hide." Every 
     day during the month of Elul, a trumpet is blown to warn the people to 
     turn back to G-d, except for the thirtieth day of Elul, the day 
     preceding Rosh HaShanah. On that day the trumpet is not blown, and is 
     therefore silent. This is because much about Rosh HaShanah is concealed 
     and shrouded in mystery. The mystical aspect of Rosh HaShanah is 
     indicated in Scripture: "Sound the shofar on the New Moon, in 
     concealment of the day of our festival" (Psalm [Tehillim] 81:3). 
     Satan, the accuser, is not to be given notice about the arrival of 
     Rosh HaShanah, the Day of Judgment. 

      "Rosh HaShanah is called Yom HaKeseh, or the Day of the Hiding, 
      because it was hidden from satan (Ha satan), the adversary. The 
      Bible says that satan comes to rob and to steal (John [Yochanan] 
      10:10, and to confuse (1 Corinthians 14:33). Because it is the Day 
      of Judgment, it is symbolically hidden from satan (satan did not know 
      and understand the plan of the cross [tree], First Corinthians 2:7-8). 
      This was hidden from him as well. Believers never said when the day of 
      Rosh HaShanah was; they simply said, "Of that day and hour no one 
      knows, only the Father." 

      "One of the reasons most often given to disclaim that the resurrection 
      of the dead and the catching away of the believers is on Rosh HaShanah 
      is the statement given by Yeshua in Matthew (Mattityahu) 24:36, as it 
      is written, "But of that day and hour knoweth no man, no, not the 
      angels of heaven, but My Father only." Because Rosh HaShanah was 
      understood to be the hidden day, this statement by Yeshua is actually 
      an idiom for Rosh Hashanah. Thus it should be given as proof that He 
      was speaking of Rosh HaShanah because Rosh HaShanah is the only day 
      in the whole year that was referred to as the hidden day or the day 
      that no man knew. 

(http://www.geocities.com/Heartland/2175/chap7.html#CHAP7)

Moza