What the Bible says about In God
(From Forerunner Commentary)
Being in or in union with God does not mean to be bodily inside of each other, because in all the verses that describe people who were "in" another, they had bodies of their own. So being in means "joined with" toward the accomplishment of the same purpose, and in our case, it is for the fulfilment of God's purpose that we are in union with Him.
John W. Ritenbaugh
Image and Likeness of God (Part Four)