I think the word Son is a biological relationship, as Jesus was conceived by the Holy Spirit, as John 3:16 "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
As Jesus was the Son of God and Word of God, the prophet's only could tell what they heard from Jesus, as Jesus was the Son and as he and the Father were one, his words weigh more than the prophet's or anybody else.