Why was Eve already inside Adam at creation?
Eve was already inside Adam because she had to be, so Adam could remain the federal head of the human race in salvation. Genesis 5:2 confirms this: God called their name Adam, showing Eve was part and parcel of him when God created and named him.
Les explains that Adam was alone for a period while naming the creatures, and God had already said it was not good for man to be alone. God caused a deep sleep to fall on Adam, took a side chamber, which is the same definition as the Hebrew word for rib, made the woman, and brought her to the man. Les then turns to Genesis 5:2 to show this is exactly how it happened: male and female He created them, blessed them, and called their name Adam. This indicates Eve was already inside Adam to a certain degree. She had to be, in order to keep Adam as the head, the federal head of the human race when it came to salvation. She was part and parcel of him even as God created him and named him Adam.