A day the Lord has made

 
                                                          Genesis 1:1

                           In the beginning, God created the heavens and the earth. ... Genesis 1:26-27 Then God said, "Let us make man in our image, after our likeness. And let them have dominion over the fish of the sea and over the birds of the heavens and over the livestock and over all the earth and over every creeping thing that creeps on the earth."
  So God created man in his own image, in the image of God he created him; male and female he created them....  Genesis 1:31 And God saw everything that he had made, and behold, it was good.  And there was evening and there was morning, the sixth day. 

        Genesis 2:2,3  And on the seventh day God finished his work that he had done,  and he rested on the seventh day from all his work that he had done.

       So God blessed the seventh day and made it holy, because on it God rested from all his work that he had done in creation.