The children of the flesh are just like dog's,
Matthew 7:6 Give not that which is holy unto the dogs,
they have no faith or loyalty, a dog will leave you for a piece of meat or food, just like a person of the flesh has no loyalty except to his material needs or carnal needs, like a dog they do not have the Holy Spirit!
Romans 9:8 That is, They which are the children of the flesh, these are not the children of God:
John 6:63 It is the spirit that quickeneth;