Jesus tells them: "I am the true vine, and my Father is the husbandman" (v.1).
The Lord in the Old Testament uses this simile to refer to his people Israel (Psalm 80: 8, Isaiah 5: 1-7, Jeremiah 2:21), who gave him wild grapes.
But now, at the end of time, the God and Father has grafted us to the Gentiles in the "True Vine" that is His Son Jesus Christ, through faith. There is no other "true vine" that can give the pleasing fruits to the Father, nor is there another laborer who knows the proper care of that vine and its branches than the Father himself.