For “he has put everything in subjection under his (autou | αὐτοῦ | gen sg masc3rd) feet.” Now when it says that “everything has been put in subjection,” it is clear that this does not include the one who put everything in subjection to him (autō | αὐτῷ | dat sg masc3rd).
Reference
1 Corinthians 15:27
Sequence
2974