God is described as creating many things in B'reshis chapter 1: animals, people, stars, plants, etc. However, about only five of his creations does it say that he called them by a name:
Why did he name those creations, and no others?
Rambam gives his explaination in the Guide of the Perplexed, Book 2, Chapter XXX:
It is also important to notice that the words," And God called a certain thing a certain name," are invariably intended to distinguish one thing from others which are called by the same common noun.
The first Choshech, in verse 2 (וְחֹשֶׁךְ עַל פְּנֵי תְהוֹם), denotes the element fire, where as in verse 5 (וְלַחֹשֶׁךְ קָרָא לָיְלָה) Hashem uses Choshech the way we typically use it, the sense of "darkness".
The element fire is called Choshech because it is not luminous, it is only transparent; for if it were luminous we should see at night the whole atmosphere in flames.
We must further consider that the term erez is a homonym, and is used in a general and a particular sense.
There is one common element of "water" which is distinguished into three forms: seas, firmament and 'over the firmament' (water by name, but not form). "Water" in the first verse (אֵת הַשָּׁמַיִם וְאֵת הָאָרֶץ), does not refer to the water which forms the seas, I think "fluid" would be a better translation for the first "water", while "water" in verse 10 (וּלְמִקְוֵה הַמַּיִם קָרָא יַמִּים), the water in the seas, is ordinary water.
The phrase," And he divided between the waters," etc., does not describe a division in space, as if the one part were merely above the other, whilst the nature of both remained the same, but a distinction as regards their nature or form.
The sefer גבעת שאול here explains that when there are two things mixed together, for example apples and oranges, and one wishes to separate the apples from the oranges, there are three ways to do it. The first is by taking all the apples, leaving the oranges where they are. The second is by taking the oranges, leaving the apples where they are. And the third way is by moving both the apples and the oranges to different places, and this is the most complete and decisive separation.
Here too, these five things that Hashem gave names to during the six days of creation were things which were originally mixed together under a certain name, and after they were completely and decisively separated Hashem gave them new names to show that their separation was to be forever, and that they would never go back to being a mixture.
The first of these things were light and darkness, which operated in a mixture without any order, until Hashem separated them and gave each one its own spacial and temporal rules, and He then called the light 'day', and the darkness 'night'. Similarly, the whole world in the beginning was a mixture of water with water, but then Hashem separated the upper waters from the lower waters and called the firmament and the upper waters 'heaven'. But the lower waters still operated in a mixture with the earth, so Hashem made a second separation, gathering the lower waters into one place so that the dry land appeared, and He called the dry land 'earth' and the gathering of waters He called 'seas'.
There is also a sixth thing that Hashem gave a name to during the creation, and that is the name He gave to the male and female together, as it says in Bereishis 5,1 "Male and female He created them and blessed them and called their name 'Adam', on the day when they were created". Here however He made a change from the previous namings, because before they were separated they were also called 'Adam'. But in order that their separation would not be a total disassociation but rather they should be "one flesh", working together in the completion of their task in this world, He did not give them a new name but again called them 'Adam', continuing with the first name.
Rav Samson Raphael Hirsch explaines the phrase “ויקרא ל…” not as “God named” but as “God assigned”. Light was not called “Day”; rather, it was given purpose as enabling daytime.
