What does it mean to be a son? Scripture uses the word in several ways: a son by birth, as every creature brings forth after its kind; a son by association, as we speak of a son of a nation or a school; and a moral son, as when Paul calls Elymas a son of the devil and Jesus calls Judas the son of destruction. In every case a son reflects his father. Adam fathered Seth in his own likeness, and a tree is known by its fruit.
That is why Jesus could tell those who claimed Abraham as their father that their works showed another father. Man's sonship and sonhood, his standing and his way of life, are by nature those of the devil, and the works of the flesh prove it. Those who do such things will not inherit the kingdom of God.
Our hope is adoption through Christ. God gave His only begotten Son, unique in kind, and in love predestined us for adoption as sons through Him. Christ emptied Himself and became obedient to the point of death; God made Him who knew no sin to be sin for us, so that by one man's obedience many are made righteous and accepted in the Beloved. Our sonhood is then lived out by the Spirit: all who are led by the Spirit of God are sons of God, crying Abba, Father, and bearing His fruit. The sermon closes at the vine: abide in Christ, for apart from Him we can do nothing.