Image is everything
God created mankind in
His own likeness
Then God said, “Let us make mankind in our image, in our likeness, so that they may rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals, and over all the creatures that move along the ground. So God created mankind in his own image, in the image of God he created them; male and female he created them..”
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God's creates mankind to bear His image
God created mankind to be relational with a special mind, will and emotions like Him and unlike other creatures. Mankind is creative, can evaluate, contemplate and make decisions intelligently and gain knowledge and wisdom. Mankind was created male and female and was created to rule over the creatures of earth.
Also, there is existing plurality and relationship with God before mankind is created, showing that mankind was not created out of desperation or loneliness but out of abundance of love. The verse does not read "I will make man in my image." Plurality is further revealed in scripture as unity in God and 3 distinct entities, Father, Son, Spirit.