Answer:
   
   The plural (for example, in Genesis 1:26) has been the source of
   wonder for most of the commenators. The following are some of the
   explanations:
     * G-d wanted to teach a personality trait to man. Therefore, even
       though He didn't require their input into the decision, G-d turned
       to the angels and asked them if they would participate. This act
       of respect thereby became a fundamental feature of human
       composition.
     * There are more than one Hebrew nouns that end in "-im" that are
       not plural. For example, Mayim (water) and Chayyim (Life). The
       same is true of Elohim. Sometimes the "-im" ending is used to
       connote power, not plurality. Whatever the grammatical origin of
       this word, it is used in the Hebrew Bible as a *singular* noun.
     * Some scholars view the use of Elohim as a plural that expresses an
       abstract idea (e.g., zekunim, "old age"; neurim, "time of youth"),
       so that Elohim would really mean "the Divinity."
     * It might come from historical usage in the language at the time.
       It may be derived from Canaanite usage, and the early Israelites
       would have taken over elohim as a singular noun just as they made
       their own the rest of the Canaanite language. In the
       Tell-el-Amarna Letters Pharaoh is often addressed as "my gods
       [ilaniya] the sun-god." In the ancient Near East of the second
       half of the second millennium B.C.E. there was a certain trend
       toward quasi-monotheism, and any god could be given the attributes
       of any other god, so that an individual god could be addressed as
       elohai, "my gods" or adonai, "my lords." The early Israelites felt
       no inconsistency in referring to their sole God in these terms.